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1. 9 5 Description of Schematics ccceecceseeesseeeeeeeeeneeeeneaeseseeeenseeeeeeeeesaaesaseeeeneeeeseaesaseeesaaeeeeseeseseaeseseeeenseeeneas 9 6 Schematic name QMSE T1 scccsecessscesseeeneeeeeeeeeeseaesesneeenseeeseeesesaaesganeesnseeeseaeseseaesaseaeeeeneeeeas 9 6 MICrOptOCeSSOE err ete degeret EEN EE EC 9 6 Digital VO e E 9 6 The LED pott oraha rae dm ee Pot qe cb PR ER Me o elders 9 7 he SNIP XP Ort reete tete tete iiie tei eter be m net De Be 9 7 Phe MISC E 9 7 eru CERRO 9 7 RS232 I ntetfaces 5c ee e RR ne CER TRO gege alee 9 8 Schematic name QMSE Tee eeeeeeesesenee essen nene snnm nnmnnn mnnn sn nm nr nnne nnn rn sn nnns 9 8 I V caliDratiOn Nee eebe ete t ert ft eet E ode o erroe e SEA EE Php ta Leto Edge 9 8 RRE e EE 9 8 Power up Conditioning ENEE erp eH Reo et Ee ete Le Dee es 9 9 Schematic name QMSE T3 uei cuisse ied cd ents de aed edn ek Gane 9 9 DC Control AN Olne eegene e ete etie etd de 9 9 RF Amplitude Detection 2 nte ed eie ER RE ee E ete eerie eto 9 10 RE Amplitude Control 2 tim Redeem esi etel re ee ec dE 9 10 Foldback Current Limatirnig tdt Eed 9 10 Schematic name QMSE B1 Sege ugeet cuoc cte va ccce ENEE ee EAR See Eug 9 11 Mass filter RE Supply x iue dete e a er ettet tee cu eet E i ee 9 11 DC Potentials i2 eet ete eee tete ere he ceterae esee dena es cee eut 9 12 Schematic name ONSE B2 ieg
2. EN 5 59 Liner iniuria cemere 5 60 C EE 5 60 DlIpar m param 0 255 5 aui ede eet rr EEG E p PEE CE RARE ERE Cete leen boda 5 60 DSparam param 0 8500 40 8500 7 5 61 RIparam param 86 0000 86 0000 none 5 63 RSparam param 600 0000 1600 0000 none sse 5 64 Error Byte Definitions eeeeeeeeeeeeeeeeeeen ee eeee enne nnne nnns nn nn nnnm n nasa nnmnnn sanies sane nnn 5 66 Chapter 6 Tuning 6 1 Introduction E 6 2 MUNIN oT i e Fre ERES 6 4 Peak Tuning ProceduUre e eene gees EES 6 5 Iotroduetton m X 6 5 General Procedure EE 6 6 Peak Position Tuning Algorithms neeeeeeeeeeeeeeenee enne en nennen nnne nnn nnne nnn nannten nnn 6 7 Peak Width Tuning Algorithms eeeeeeeeeee eene nennen nenne nnne nnn nnne nnmnnn inan neni nn 6 9 CIS Quadrupole Gas Analyzer viii Contents Temperature effects on the mass scale calibration esee 6 10 Sensitivity Tuning Procedure Seeerei 6 12 Electron Multiplier Tuning Procedure eeeseeeeeeeeeeee enne nnne nennen nnn nnne mnnn 6 15 Chapter 7 Maintenance 7 1 LENDDIie e 7 3 Probe Bak eu Aere ee 7 5 Procedute oed ee ee tacce res tire IE EAE TIE 7 6 lonizer Replacement
3. 1 2 Standard Equipment Supplies 1 2 ERNEIEREN e Ee Ee ee Ee petu eei 1 3 Optional Equipment E 1 3 IC ru e EE 1 4 nig roi e 1 4 Pressure Reducing Gas Inlet System eeeeeeeesesseseeeee eene nnn nnne nnn 1 4 Probe Installatlon ee EE 1 5 Hardware Requirements tete ertet c p t e et ue obo 1 5 Procedure 5 ne p eR e td ie a ue e ver eu Pate e I a B NEUE eo Pads 1 7 Pumping System Installation neeeeeeeeeiee siens eene teen nnnm nn nnn nn natn n annee inna 1 7 Electronics Control Unit Installation esses eiie eene eene nennen nnn nennen nnn 1 8 Hardware Requirements edendo eie ette etit retire eee ve eee ng Pepe EE 1 8 ere UE 1 10 RGA Windows Installation eeeeeeee eee eeeis esee eene nenne nnn n natn n nnn nn ansa sinn nnn annene 1 11 Minimum System Requirements Single Head Operation see 1 11 enge 1 12 Turning on the CIS Analyzer eeeeeeeeeseeseees eise nee nennen nant nn nn tnn nnn tn ansia nasa sa sn nn sn nnns 1 12 Running the CIS Quadrupole Gas Analyzer sseeeseeeeeeeeeeses esee nennen nnn nn ann nant nant nnn 1 13 CIS Quadrupole Gas Analyzer 1 2 Unpacking Unpacking Before You Open the Box 1 Checklist Please read and follow all installation inst
4. eeesseeeeeeeeeee ENEE en enne tennis nn tnn nn nn 1 13 Chapter 2 General Operation 2 1 The SRS Closed lon Source Quadrupole Gas Analyzer eese esee enne 2 2 Basic Data Acquisition Modes 1 eeseeeeeeeeeeeeee eese eene nnne nnn nn nnn inset tn inse nn tn nnmnnn annn 2 5 Principles of operation 11eeseeeeee esee eeeennee eene nn nnne nnmnnn nnmnnn nnmnnn nnmnnn nennt 2 5 The CIS Analyzer as a Mass spectrometer eeeeeeeeeeseeseeee einn en nennen nnn nennen nnne nnn 2 6 The CIS Analyzer as a Single Gas monitor esee eeeeeeeeeeenne nennen nnne 2 7 Basic Operating Mod ES aai a r aara Tea a raare e sana ea a nin tn assa ta sisi s natn ns sa sa ss sms aaiae 2 8 RGA Mode UHV lt P lt 10 Tor 2 8 CIS Mode 10 lt P lt 10 TOIT eto endete secuti Ge tuu eeu eR D LUE 2 9 Contents v High Pressure Sampling P gt 1 MTOrr sssssssssssunsuunnuunnuunnununnnnnnnnnnunnnunnnunnnunnnunnnnunnnnnnnnnnnnnnnnnnnnnnnnnn annnm aaa 2 11 Partial Pressure Analysis Basics cccccseccceeseeseeeeeeeseeeeneeseeesneeseeeeneeseeeeneeseeesneeseeesneeseseseeseeeenenseesenes 2 12 How Mass Spectra are Interpreted usseeeeeeeseessees essen enne enn nnne nnnn nnns 2 12 Partial Pressure Measurement eese essen eene nnne nnne nennt nnn nn nnn r nnmnnn nnne nnne 2 13 Partial Pres
5. 7 13 mitai ul E e E 7 13 Contamina N mI 7 13 lte LEE 7 14 CDEM Pre conditionifig EEN 7 15 CDEM Refreshment oz oe ee ee AE NEEE sua Eana stavesebecetudiecedvevanstetbecrendues 7 16 Natierlech 7 16 Proced le Lettere ILI Guu eer cece EEN EE Ee 7 16 CDEM Replacement 2 1 Iit ctae puc ceci baaa cc eoru done roue c cp aote sucus EENS 7 17 CIS Quadrupole Gas Analyzer 7 2 mum 7 17 Procedure ss ccd tease toed aei duce rati ee ducc chine uL 7 17 Quadrupole filter cleaning neeeeeeeeeeee eise eeenenee enne eene nnne nennt nnn nasa sna sane nsn tn nass s assa natn Rusa 7 20 d HIN EE 7 20 Procedure 2 2324 EE EE EE 7 21 SRS Probe Refurbishing Service eese iiesieees essen eene nn sena snnm h nn nn nn nn nn assa nasi a anneanne 7 24 CIS Quadrupole Gas Analyzer Warnings 7 3 Warnings The service information in this chapter is for the use of Qualified Service Personnel To avoid shock do not perform any procedures in this chapter unless you are qualified to do so Read and follow all Safety and Precaution warnings before servicing the product Dangerous voltages capable of causing injury or death are present in this instrument Use extreme caution whenever servicing any of its parts Carefully follow the instructions in this chapter Failure to do so might result in
6. 2 2 22 1 cc SEENEN CERS EENS ES 7 7 Equipment eS a Tee ee 7 7 Procede mese RE Nee EE 7 7 Filament Replacement 2 ege Ee 7 10 Handling and care of the filament eeseeeeeeeeeeeseeeeene seen ennt 7 10 nnn ee 7 10 Procedure hun Ee 7 10 CDEN Handling and Care eeeseeeiieeeiseeeeeseeeeeen seen nena nnn n Eaa sas a natn Rn sn snas satanas m sse aeii 7 13 Handling and mounting eeeeeeeeeeee eene eene nn nnn nnn h anne nn hin nn nnn anie nn rinse nnne 7 13 Operating pressUre 2 32 21 2 12 Ie neta aiden SES 7 13 Operating temperature ueesesieeseeeeeeeeeseeeee nennen nnne nn inna ansa sane nsn tn nasa sans sanas nasa nnns 7 13 Bakeout temperature e eeeeeeeeeeeeeeeeeeeen eene nennen nnnm nn nnnm nsn sn nna asse nenna nnmnnn asse nnn 7 13 Operating voltage 2 1i Iesse hacen dian aa Aap tee heat 7 13 Initial PUM P GOWMN e 7 13 Contaminatiom ees Ee ee E 7 13 tel me e E A E ene ce steed tude ben teat ceus A TT 7 14 CDEM Pre COnditioning ov ssccciscceccsccesecercsctesencecccetecten piece ae SEENEN EENEG SEENEN 7 15 CDEM Refreshment 12 Lo eta oes cae rudi encase ea a eae 7 16 Materiile Geer ee Ee AE 7 16 Proced te 2 nu ee 7 16 CDEM Replacement Lon tette eed M E AD
7. Description Mass Lock Description Calibration Enable Query DI parameter Peak Width Tuning DS parameter Peak Width Tuning RF Driver 90 amu Peak Position Tuning RF Driver 128 amu Peak Position Tuning Error Reporting Name ER EP ED EQ EM EF EC Description STATUS Byte Query PS ERR Byte Query DET ERR Byte Query QMF ERR Byte Query CEM ERR Byte Query FIL ERR Byte Query RS232 ERR Byte Query Parameters 0 0000 M MAX Parameters 9 0 255 2 5500 2 5500 86 0000 86 0000 none 600 0000 1600 0000 none Parameters eO zl 03 02 02 cl sl Note M MAX 100 for CIS100 200 for CIS200 and 300 for CIS300 Echo none Echo Query response Query response Query response Query response Query response Echo Query response Query response Query response Query response Query response Query response Query response Chapter 1 Getting Started This chapter describes the process of unpacking checking and installing the SRS CIS Analyzer on a vacuum system Please read and follow all installation instructions to insure that the optimum performance of the instrument is not compromised during the installation process In This Chapter Unpacking 1 2 Before You Open the BOX csetezcoceedacececcdecctaceensedecatseeudesetedecegecseaceeetececescucssasesececsducee se 1 2 CHECKS
8. No Not Applicable SRS will not service any equipment that might potentially be harmful to its service personnel SRS will not accept any equipment which has been radioactively or explosively contaminated without written evidence that such equipment has been properly decontaminated Legally Binding Declaration I hereby declare that the information supplied on this form is complete and accurate The dispatch of equipment will be in accordance with the appropriate regulations covering Packaging Transportation and Labeling of Dangerous Substances Name print Job Title Organization Address Telephone Fax Legally binding signature Date Stanford Research Systems 1290 D Reamwood Ave Sunnyvale CA 94089 Ph 408 744 9040 FX 744 9049 Glossary of Terms The following is a listing of some of the most important terms used throughout the SRS RGA Operations Manual For a more complete listing of terms relevant to partial pressure analyzers in general refer to A Dictionary of Vacuum Terms used in Vacuum Science and Technology Surface Science Thin Film Technology and Vacuum Metalurgy edited by M S Kaminsky and J M Lafferty published by the American Vacuum Society 1979 A Basford et al J Vac Sci Technol A 11 3 1993 A22 40 Recommended Practice for the Calibration of Mass Spectrometers for Partial Pressure Analysis Update to AVS Standard 2 3 Anode Grid Ionizer Compon
9. Pumping system ECU dimensions LED indicators Computer interface Software Power Requirement Weight Warranty High Conductance Closed Ion Source 0 4 L s Gold coated 304 stainless steel Electron impact ionization Tungsten standard or Thoriated Iridium optional with firmware protection Field replaceable 15 to 105 eV programmable 4 or 8 eV programmable 0 to 150 V programmable 0 to 1 0 mA programmable 8 75 from feedthru flange face to top of CIS Port 2 75 CF 2 75 CF An oil free turbopump based system with a minimum pumping speed of 40 L s 1 and a base pressure better than 2 10 Torr is recommended to meet the instrument s specifications 9 1 x 4 1 x 3 1 Easily separated from the probe for bakeout Power ON OFF Filament ON OFF Degas ON OFF Elec Mult ON OFF RS 232 Busy signal Error Leak and Burnt Filament RS 232C 28 800 Baud with high level command set and fully enabled RTS CTS handshaking Windows OS based application Requires 486 66MHz PC or faster 24 VDC 2 5 Amps Male DB9 connector Optional 110 120 220 240 VAC 50 60 Hz built in power module 7 lbs One year parts and labor on materials and workmanship CIS Command List Initialization Name Description ID Identification Query IN Initialization lonizer Control Name EE FL IE VF Description Electron Energy Electron Emission Current Ion Energy Extraction Plate Voltage Dete
10. The RGA s resolution is sufficient to clearly distinguish peaks that are 1 amu apart They are designed for the analysis of the gases present in high and ultra high vacuum systems The specifications of the RGA are a perfect match for vacuum diagnosis Not many materials with a mass greater than 200 amu will be volatile and so a small mass range is suitable The high resolution of a research grade mass spectrometer is not necessary for the analysis of low molecular weight species Overall RGA s are affordable instruments that can be permanently attached to a vacuum system Experiments and processes are performed under vacuum for two main purposes to lower the total pressure to a suitable level and to provide an extremely clean environment An ion gauge addresses the first purpose but only an RGA can address the second The high sensitivity of some processes to specific impurities makes the goal of cleanness more difficult to achieve than the required total pressure A typical method of making a system cleaner is to lower the total pressure The assumption being that the partial pressure of the impurities is directly related to the total pressure This assumption fails in two ways First it is simply not true a total pressure measurement cannot tell the user tell the user the level of impurities As an example a system operating at a total pressure of 1 1 x 10 mbar might consist of 1 0 x 10 mbar of water due to outgassing and 0 1 x 10 mbar
11. fugitive leaks appear and disappear at a specific fitting What is happening is that the test gas is inadvertently flowing to another fitting which has a real leak Whether this inadvertent gas flow occurs depends on exactly how the test gas is applied to the fitting with the fugitive leak Small air currents caused by equipment fans or ventilation systems can move the test gas in unpredictable ways Confining the test gas to the fitting under question can help but the RGA provides a easier solution use a gas other than helium Helium will spread in air quickly and diffuse into many fittings A heavy gas like argon or tetraflouroethane is far easier to confine to a specific fitting Once the moderate leaks have been located and eliminated a follow up with helium to check for tiny leaks is warranted Bellow Valves Bellow valves can be difficult to leak test due to the large volume of gas contained between the bellow and the valve body To perform a quick leak test it is required to change the composition of the gas in this trapped volume quickly Unfortunately for some valves this volume of gas is not highly accessible This greatly reduces the response time of a leak test For a leak causing a base pressure of 10 mbar in a vacuum system with a 701 s pump the volumetric flowrate of gas entering from the atmospheric side of the leak is 7 nanoliters per second For a bellow with a trapped volume of 1 ml trapped the response time con
12. Additional vacuum hardware is usually required to accommodate the extra gauge Under normal operating conditions i e gas pressure 10 Torr in the process chamber and a well matched pumping system the pressure on the quadrupole rods should be approximately two decades lower than the chamber pressure i e 1 210 Torr The following table is a compilation of the minimum requirements that the Pumping System must satisfy in order to be properly matched to the CIS Analyzer Whenever applicable a recommended spec is also provided CIS Quadrupole Gas Analyzer Pumping System Requirements 3 23 Pumping Speed see Note 1 Le A0 70 Inlet Flange n a CF 2 75 O D CF 2 75 O D Start up time sec Cooling requirements Natural air convection or forced air Notel The effective conductance at the ionizer s inlet i e considering the length of tube and the two holes in series is approximately 0 4 L T This value indicates that a 100 fold pressure differential between the ionization volume and the quadrupole volume can be established simply connecting the CIS analyzer to a pumping station capable of delivering an effective pumping speed of at least 40 Ls at the filament and quadrupole rods These pumping speed levels can be accomplished with even some of the smallest turbomolecular pumps that are currently available A large increase in effective pumping speed at the ionizer cannot be expected by increasing the size of the turbo pump abo
13. LED s while operating the instrument e Diagnose and troubleshoot problems as soon as they are detected CIS Quadrupole Gas Analyzer 8 4 Internal Error Detection in the CIS Analyzer e RGA Windows users Use the Retry button of the Error Report Window to trigger one or two fresh error checks on the hardware before declaring a problem Programmers Repeat the query command if a problem was detected after the last query Note that the values of the Error Bytes often change after an Error Byte query command is executed Some query commands update the byte value after performing a fresh test on the hardware while others clear error bits after they are read to provide a clean error reporting slate Please see the Error Reporting Commands list for details e Communications errors are different from hardware errors in that the Error LED only flashes two or three times when the problem is detected RGA Windows reports communications errors very explicitly as soon as they are detected Programmers will need to use the EC command to diagnose the problems e Programmers should consider having their software automatically report the Error Code for each problem detected e Use the Get Head Info command in the Head Menu of RGA Windows to get a complete listing of all the Error Bytes at any time CIS Quadrupole Gas Analyzer Basic Troubleshooting 8 5 Basic Troubleshooting A unique Error Code has been assigned to each
14. Line Cord Service Fan Dangerous voltages capable of causing injury or death are present in this instrument Use extreme caution whenever the instrument cover is removed Do not remove the cover while the unit is plugged into a live outlet The CIS Analyzer s built in power module option Opt02 has a detachable three wire power cord for connection to the power source and to a protective ground The exposed metal parts of the instrument are connected to the outlet ground to protect against electrical shock Always use an outlet which has a properly connected protective ground Do not attempt to service or adjust this instrument unless another person capable of providing first aid or resuscitation is present Do not install substitute parts or perform any unauthorized modifications to this instrument Contact the factory for instructions on how to return the instrument for authorized service and adjustment The fans in the CIS Analyzer are required to maintain proper operation Do not block the vents in the chassis or the unit may not operate properly CIS Quadrupole Gas Analyzer iv Contents Contents Safety and Preparation For Use ssseesieeeieeeeeeeeeeeeee eene nennen nin nn ansa sinn nsa tn nasa snas sans ann n nsn nn ns iii CONTEC INES eR DE iv TE ree M xi CIS Command Erg c xiii Chapter 1 Getting Started 1 1 M
15. Mode of operation are used as conversion factors between the ion currents received form the head and the pressure units selected by the user The sensitivity factors are measured with the Faraday Cup detector and can be updated or changed very easily using the Sensitivity Tuning command in the Head menu A separate Electron Multiplier Gain Factor stored in the non volatile memory of the CIS Head is used to correct the ion signals for the gain of the electron multiplier The gain of the electron multiplier is highly mass dependent and defined relative to the corresponding FC signal An automatic Electron Multiplier Gain Adjustment command built into the program can adjust the CDEM voltage for any gain between 10 and 10 Consult the RGA On Line Help Files for details on the automated tuning procedures built into the RGA Windows program Also see the Sensitivity and Electron Multiplier Tuning sections of the Tuning Chapter for more general information The Table mode of RGA Windows offers scaling factors for all of its channels eliminating the limitations imposed by the single sensitivity factor on multiple partial pressure calculations For example the scaling factors can be used to display correct partial pressure for all the species in a table if the ratios between the partial pressure sensitivities of the different components are known and only principal mass peaks are used to monitor them The scaling factors can also be CIS Quadrupole Gas
16. RI Am RS 128 Notes e The new RI value must fall within the acceptable parameter range of the RI command e This change mostly affects the position of the peaks at the low end of the spectrum e A decrease in RI shifts the low mass peaks to the right peaks show up at higher masses an increase in RI shifts the same peaks to the left peaks show up at lower masses High Mass Peak Position Adjustment To displace a high mass peak mo by a distance Am amu in the mass axis modify the value of RS from its original value RS to RS RS mo motAm Notes e The new RS value must fall within the acceptable parameter range of the RS command e Modifying RS affects the spacing between peaks in the spectrum An increase in RS results in the peaks getting closer together and a decrease in RS results in the peaks getting further apart from each other e The effect is more significant at the higher masses and should have very little effect on the position of the low mass peaks that is why you do this adjustment second CIS Quadrupole Gas Analyzer 6 8 Peak Tuning Procedure e The lower the mass to charge ratio of the low mass gas the less this adjustment will effect the position of its peak e See that a decrease in RS results in the high mass peaks moving to higher masses right shift and vice versa Iterations In most cases it will be necessary to repeat the two position adjustments one or two more times until both
17. and 215 Vdc on the other The frequency of operation of the mass filter is the same for all models and is fixed at 2 7648 MHz by an internal clock The rod structures in the mass filter are primarily capacitive so to reduce the circuit drive requirements the rod reactance is resonated with an inductance The advantages of this resonant drive circuit is the primary reason for operation at a fixed frequency Important The CIS Cover Tee i e stainless steel tube that encloses the quadrupole filter assembly contributes to the overall capacitance of the rod assembly and should not be removed from the probe Failure to operate with the CIS Cover Tee in place will push the driving circuit out of resonance and will limit the operating mass range of the filter The internal calibration parameters used by the microprocessor to set the RF DC levels during scans and measurements are pre programmed at the factory as part of the test and calibration procedures performed on the instrument before shipping However the parameters can be readjusted easily and whenever necessary using the Peak Tuning procedures described in the Tuning chapter CIS Quadrupole Gas Analyzer 4 12 Maintenance and Service Maintenance and Service e The ECU box does not have any serviceable parts and does not require any routine maintenance e Do not perform any unauthorized service adjustment or modification of the instrument e Do not install any substitute part
18. lt LF gt terminator No errors are present as long as the byte value is zero If one or more bits of the STATUS byte are found set the specific error bytes PS ERR DET ERR QMF ERR CEM ERR FIL ERR and RS232 ERR must be queried individually to diagnose the problem Consult the Error Byte Definitions section of this chapter for detatils on the different error bytes of the CIS Analyzer Consult the Troubleshooting chapter of this manual for possible causes and solutions to any problems reported Important Since internal checks are constantly being performed within the CIS Head the STATUS Byte should be queried regularly by the programming software to detect any possible problems Parameters This command is a query and can only have one parameter format ER Error checking The only acceptable parameter is a question mark The absence of a parameter i e ER is treated as a bad parameter error CIS Quadrupole Gas Analyzer Tuning Commands 5 59 Tuning Commands CE Description Calibration Enable Query Echo JP100 setting Query the Calibration Enable Disable jumper JP100 status An internal jumper JP100 on the digital i e top electronics board of the ECU box can be configured by the end user to enable disable the modification of the peak tuning parameters The CE query command returns the JP100 setting in ASCII format with a lt LF gt lt CR gt terminator The two options for the query response are 0 JP1
19. serious personal injury and damage to the instrument Do not substitute parts or modify the instrument Because of the danger of introducing additional hazards do not install substitute parts or perform any unauthorized modification to the product Do not use the product if it has unauthorized modifications Return the product to SRS for service and repair to ensure that safety features are maintained Use only SRS supplied replacement parts Disconnect the ECU box from the probe before servicing any of the probe components Turn off the emission and wait for at least 30 minutes before removing a probe from a vacuum chamber Serious burns can occur if the probe components are handled too soon Use proper vacuum procedures when handling the probe Avoid contaminating the probe e Work in a clean dust free area A clean room compatible environment is best Do not talk or breath on any of the parts Wear gloves Use clean tools during service procedures Wear face masks hair covers and no facial make up Protect the integrity of the vacuum seals e Avoid scratching the metal seals e Do not use nonmetal seals Verify that the vacuum port is electrically grounded before attempting installation of the CIS Head to the vacuum system CIS Quadrupole Gas Analyzer 7 4 Warnings e Stanford Research Systems does not guarantee that the cleaning procedures described in this chapter will completely remove contamination from the
20. simple form a PRGIS consists of a restriction that when placed between the gas chamber and the CIS Analyzer keeps the ionization region at a suitable operating pressure i e 2 mTorr Common restrictions used to create pressure differentials are pinholes and capillaries PRGIS s are available directly from Stanford Research Systems Please consult the factory or your local representative for information on this optional equipment However due to the large number of highly specialized applications of CIS Analyzers it is not uncommon for some users to design their own custom made inlet systems In addition to achieving the desired pressure reduction the design of a PRGIS should provide for a fast response and high signal to background ratio At pressures common to many vacuum processes i e 10 mTorr to 10Torr a simple aperture based PRGIS is suitable At atmospheric and higher pressures a two stage reduction based on a capillary and aperture should be used A carefully designed system with minimized internal surface area and vacuum compatible components will provide the lowest background contribution to the signal In order to keep the versatility of the CIS Analyzer intact SRS recommends that the restriction be part of a dual path inlet system configuration so that the ionizer can still be exposed unrestricted to the process pressure during RGA Mode operation Users designing their own inlet systems will need to know that the no
21. 0 1 This is important to assure that the magnitude of the RF for the two secondaries will be very nearly equal Silver plated Teflon coated wire is used for the secondaries to reduce skin effect losses and to minimize interwinding capacitance and to reduce the loss tangent in the dielectric Primary Drive The square wave voltage drive is provided by a pair of IRF510 MOSFETS Q402 and Q403 Theses FETs have delay and transition times on the order of 25 ns and are operated as switches The gates of the FET s are driven by complimentary square waves at 2 7648MHz with 50 duty cycles from U401 an SN75372 Each FET is on for about 180 ns The amplitude of the square wave drive is controlled by the DC supplied by Q401 a D44VH10 high speed npn power transistor The op amp U400 integrates the error signal from U306 on the top PCB to maintain the detected RF equal to the signal RP SET from the 18 bit D A The primary current is passed through the FET s 0 259 source resistor The voltage across this resistor is amplified by U402B and may be read by the CPU Approximately 1 5A is required to generate 2568V pp required at 300 amu CIS Quadrupole Gas Analyzer 9 12 Description of Schematics At low drive levels the charge injected via the gate source and gate drain capacitances of Q402 403 are a significant source of error To compensate the network of R413 R414 and C406 couple a signal with the correct amplitude and phase into the primary dr
22. 10 A Torr before the unit is shipped out Please consult the General Operation Chapter of this manual for details on the Basic Operating Modes of the CIS Analyzer CIS Quadrupole Gas Analyzer Parameter Storage Commands 5 53 Important The numeric values stored in the Parameter Storage Table are not used internally by the CIS Head in any way during operation They can only be used by the software programs that operate the CIS Head from the host computer Parameters XV0 4 99999 9999 The parameter is the numeric value that is programmed into the Parameter Storage Table at the location previously specified with the XA command The XA pointer is erased at the end of execution so that an XA command needs to be strictly used before every XVparam action XV Query the table value previously pointed to by XA The XA pointer is erased at the end of the query so that an XA command needs to be strictly used before every XV Error checking Parameter must be within specified range No default value is available CIS Quadrupole Gas Analyzer 5 54 Mass Filter Control Commands Mass Filter Control Commands MLparam param 0 0000 M MAX Description Mass Lock Echo none Activate the quadrupole mass filter QMF and center its pass band at the mass value specified by the parameter The QMF is parked at the mass requested but no ion current measurements take place The parameter is a real number and the mass increments are
23. 4 0E 08 3 5E 08 3 0E 08 2 5E 08 2 0E 08 L5E 08 110096 100 1 0E 08 5 0E 09 0E 09 10 Peak lt Height D DUO Ue rr Irem IH 80 Q 8 84 86 M Q amu e lt 20 lamu Figure 6 Peak Width Measurement It is well established that the resolution attainable by a quadrupole is limited by the number of cycles of RF field to which the ions are exposed before they reach the detector In practice the minimum resolution A Mie value attainable is mass independent linearly related to the ion energy and inversely proportional to the square of the product of the quadrupole length and frequency The two available ion energy settings of the CIS Analyzer correspond to ultimate resolution values of approximately 0 2 amu 4 eV and 0 3 amu 8 eV which are well under the factory default setting and more than adequate to separate ions which differ in mass by 1 amu or less The resolving power R at a mass M is strictly related to the DC RF voltage ratio An increase in the resolving power usually results in a decrease in the effective throughput of the filter As the DC RF ratio is increased the amplitude of the ion oscillations within the filter increase and a greater fraction of the ions are lost to collisions with the analyzer rods The throughput of the quadrupole affects the overall sensitivity of the spectrometer to the mass being filtered The e
24. A The CPU sets R C low after the data is read to prepare the A D for the next conversion cycle Power up Conditioning The A D reference output 2 50VDC is amplified buffered and inverted by U302A amp B to provide system references of 4 5 00VDC These references are set to zero volts when the system is reset so that other analog signals such as the HV and filament control signals will stay at zero until set by the microcontroller The triple 2 1 analog switch U301 a 74HC4053 is used to make certain that various circuits remain off when the system is reset until the CPU can establish the system environment Upon reset the dual flip flop U300 is reset The output of the second flip flop which controls all three channels of the analog switch will return high with the second port strobe from the CPU to the MISC bits port Immediately following a reset EMIT CTL will be low to multiplex EMIT SET to control the duty cycle of the filament heater circuit directly the X5 00REFSs will be set to zero so that all the analog control signals will be zero and the output current from the 18 bit DAC which controls the RF amplitude will be shunted to ground Schematic name QMSE T3 DC Control Voltages U307 a MAX528 octal 8 bit DAC provides DC voltages to control various parameters in the system Each output has a range from 0 to 4 98V with a step size of about 19 5 mV The eight outputs and their functions are listed here RES CTL This ou
25. A D input 24VDC supply divided by 6 A D input RF primary voltage divided by 5 A D input RF primary current 1V 400mA A D input 0 VDC A D input 0 VDC A D input focus plate ion current 1V SHA A D input filament heater duty cycle 1V 20 A D input filament heater primary current 3V A Description of Schematics 9 7 In addition to the I O port on the microcontroller there are three 8 bit digital shift registers which are loaded via the SPI then strobed by a LD bit to transfer data to the parts output registers The three digital output ports are assigned as follows The LED port QO Set high to light an LED to indicate that the 24V power supply is okay QI Set high to light an LED to indicate that the filament is on Q2 Set high to light an LED to indicate that the unit is degassing Q3 Set high to light an LED to indicate that the CDEM high voltage is on Q4 Strobe high to set I V converter to LOG mode Q5 Set high to light an LED to indicate that there has been an error Q6 Set high to light an LED to indicate that the pressure is too high Q7 Set high to light an LED to indicate that the filament is burnt out The MPX port QO CAL_0 LSB of current detector calibration attenuator multiplexer QI CAL 1 Middle bit of current detector calibration attenuator multiplexer Q2 CAL 2 MSB of current detector calibration attenuator multiplexer Q3 MPX 0 LSB of 16 bit A D converter s input multiplexer Q4 MPX
26. Analyzer as the pressure at the closed source inlet goes above 2 m Torr 1 Deviations from the linear response to partial pressure appear in the current signals As the ion density starts to approach the saturation level i e as defined by space charge repulsion effects the partial pressure sensitivity starts to decrease The linearity range can be extended somewhat by further decreasing the electron emission current to reduce the ion density in the ionizing volume However as the pressure increases the mean free path for the ion molecule collisions starts to get comparable to the CIS dimensions and increasing numbers of ions get diverted and lost before they can reach the exit aperture 2 The high conductance path between the CIS and the quadrupole mass analyzer results in elevated pressures on the quadrupole mass filter and detector that are not compatible with the safe operation of the CDEM The CIS apertures were designed such that during normal operation the pressure in the quadrupole volume can be at least 100x smaller than the pressure in the ionization region Under these conditions a 10 Torr process pressure results in a comfortable 10 Torr pressure on the filament quadrupole and detector A 100x pressure drop can be achieved pumping on the CIS with an effective pumping speed of at least 40 Ls These pumping speed levels can be accomplished with even some of the smallest modern turbomolecular pumps However a large increas
27. Avoid scratching the metal seals Do not use nonmetal seals Verify that the vacuum port is electrically grounded before attempting installation of the CIS Head to the vacuum system The ECU box does not have any serviceable parts and does not require any routine maintenance Contact the factory for instructions on how to return the instrument for authorized service and adjustment CIS Quadrupole Gas Analyzer Internal Error Detection in the CIS Analyzer 8 3 Internal Error Detection in the CIS Analyzer Several firmware driven checks automatically test the CIS Analyzer when the instrument is turned on and continuously monitor the internal workings of the unit A Background Filament Protection Mode is activated when the filament is turned on to protect the delicate filament and CDEM from serious accidental overpressures Several commands can be used to trigger hardware tests on the ECU Any one of the internal checks just described can detect and report errors but it is the responsibility of the user to monitor the CIS Head for error reports Note Refer to the last section of this chapter for a listing of the built in hardware checks available in the CIS Head Important Even though the hardware tests built into the CIS Head can check the instrument for a large variety of problems they cannot detect all possible error conditions There are two ways to detect the presence of errors in the CIS Analyzer Visually In
28. Begin by using the finest abrasive which will remove the residue normally 3200 grit Then consecutively use the next finer grit down to 12000 until the metal surface has a fine polished appearance Warning Do not remove excessive material from the surface of the precision ground rods After all metal surfaces have been polished they must be cleaned to remove all the abrasive compound from their surface Begin by placing the rods in a beaker with the ultrasonic cleaner solution Note Any good quality cleaning compound that leaves no residue after rinsing is good for this job Place the beaker in the ultrasound cleaner and agitate for 30 minutes Decant off the cleaning solution and repeat the above agitation with 4 to 5 consecutive washes with distilled water to remove the cleaning solvent Following the rinses blow dry the rods with filtered dry nitrogen and then bake them out in an oven at 180 C for fifteen minutes Warning After the parts have been cleaned and baked out they should only be handled wearing powder free latex gloves Head Reassembly Only a rough outline of the complete reassembly of the probe is presented here Use the Assembly Drawing in the Probe Assembly chapter and your own notes as a visual aid during this process Begin by assembling the quadrupole mass filter Loosely attach the cleaned rods to the alumina spacers with the spring loaded perforated screws Tighten the screws following the systematic procedure descri
29. CIS Quadrupole Gas Analyzer 1 13 Running the CIS Quadrupole Gas Analyzer This section describes how to launch the RGA Windows program and start acquiring data from the CIS Analyzer An analog scan from 1 to 50 amu is executed as an example For best results the pressure in the ionization region should be between 10 and 10 Torr Important The following steps assume that all the installation instructions described in the previous section were completed and no serious problems were encountered The CIS Head should be mounted on the vacuum chamber pumped down by its Pumping System powered up and connected to the RS232 port of the IBM compatible PC computer RGA Windows should be installed in the computer and ready to run Warning Do not operate the CIS Analyzer if the pressure in the CIS ionizer is greater than 10 Torr 1 Turn on the computer and start Microsoft Windows 2 Start the RGA Windows Software To start the RGA software simply double click on the RGA icon in the SRS RGA program group created by the RGA installation program RGA Program 3 Connectto the CIS Head e Click on the toolbar s RS232 Setup button EI or select RS232 Setup from the Utilities menu e Select the port to which the CIS head is connected often COM2 e Click on the Connect button e The connection is made when the dialog box disappears the toolbar s GO button turns green the RS232 button is highlighted and the Scan and Head menu comma
30. Figure 1 is SO from SO a matching peak at 64 not shown on the figure confirmed this On occasion this peak is seen in our chambers If SO appeared in your vacuum system would you want to know In addition to these simple gases we are interested in molecules with higher weights The next two examples show how oil and solvents can be detected Oil Contamination Figure 2 contains a mass spectrum of a common contaminant of vacuum systems oil The top pane is the measured spectrum and the bottom pane is the library data SRS Residual Gas Analyzer Appendix A 5 Tor Vacuum Diagnosis izxin dimio 7 agmg Samia Tio aoa 3 amig 26m0 DN 24m0 4 ll 1 AN DE add U te AMN ol all EN tal 14 7 8 PB E D Z e BH oM F 0 B e D oT E SF A A Arme Mass Units Figure 2a Pump Oil Contamination iano Torr SP CIL hiec hanical Purnp Oil i140 am 40 So 4n Tx dn amp 40 Souda A0 3 Gm 10 3 zoo Lowo E 1 4 7 4 JD E d ZS E Z8 GI Dt FT 40 o AG 420 ZLE G EI Ga amu Figure 2b Library Pump Oil Data SRS Residual Gas Analyzer 6 Appendix A The presence of mechanical pump oil is immediately obvious The peaks at masses 39 41 43 55 and 57 are caused by mechanical pump oil backstreaming into the vacuum chamber during a load lock sequence The total pressure in the chamber was dominated by water and was less than 2 x 10 Torr In this case the total pressure might satisfy operating condit
31. If the check fails the red Error LED is turned on instead to indicate the problem Note A check on the external power supply can be performed at any time during operation using the diagnostic command EP Filament The Filament LED indicates the presence of electron emission current in the CIS ionizer It is turned on when a finite emission current is requested by the user It is turned off when the user requests a null emission current or when a filament error condition 1 e overpressure worn out or burnt filament is detected and the filament emission is turned off Note Filament error conditions are easily diagnosed with the help of the Leak and Burnt LED and the assortment of diagnostic checks built into the firmware and supported by the RGA Windows program Degas The Degas LED is not used by the CIS Analyzer ElecMult The ElecMult LED is turned on whenever the electron multiplier detector is CIS Quadrupole Gas Analyzer 4 8 Rear Panel active i e when a finite biasing voltage is applied across the electron multiplier Several different mechanisms can turn off the electron multiplier and its LED a null bias voltage request by the user and an overpressure that shuts down the filament emission RS232 The RS232 LED reflects the activity on the RS232 Transmit and Receive lines ERROR Red LED s Error The Error LED indicates the presence of errors in the operation of the CIS Analyzer Errors can originate from many diff
32. Mass Filter RF P S RF P S Error RF_CT exceeds V_EXT 2V at M_MAX M_MAX 100 for the CIS100 200 for CIS200 and 300 for CIS300 The RF P S goes out of regulation when the quadrupole mass filter is set to M MAX amu Note When RGA Windows detects an RF7 error it automatically tests the CIS Head and quickly determines the maximum mass value at which the quadrupole mass filter can be operated reliably i e without the RF P S going out of regulation If the available mass range is smaller than the user s selected scanning range a warning is immediately displayed on the PC screen The user CIS Quadrupole Gas Analyzer Troubleshooting Basic Troubleshooting 8 9 can then choose to proceed i e ignore the problem at own risk or can get information on how to Troubleshoot the problem by pressing the Help button This problem should not be ignored since it can be associated to erroneous readings at high masses e Is the quadrupole probe connected to the ECU box The ECU s RF P S cannot operate in the absence of a probe e Is the CIS Cover Tee in place The CIS Analyzer will not operate without the CIS Cover Tee in place e Are the electronics warmed up The RF P S is optimized at the factory in a completely warmed up ECU box Cold operation reduces the efficiency of the RF P S and can in some cases lead to an RF P S error To completely warm up the CIS electronics and match the factory conditions turn on the filament to
33. Parameter must be within specified range and must be an integer No default value is available XVparam param 0 0000 99999 9999 Description Parameter Value Echo Query Response Query or modify an element of the Parameter Storage Table at the table location previously specified with the XA command Important Use XA to select the correct table element in advance A Parameter Storage Table capable of storing up to 10 different numeric values i e elements is part of the non volatile memory of the CIS Head The command pair XA XV is used to update or query the elements of that table XA where A is for Address is used first to point at any one element within the table XV where V is for Value can then be used to query or update the value of the element previously pointed to by XA The numeric storage available through XA and XV is often used to store a variety of instrument specific calibration data directly into the CIS Head making the instrument s calibration independent from the host computer that controls it Important RGA Windows reserves the use of the first three members of the table XA1 2 and 3 for the storage of sensitivity factors for the three Basic Operating Modes of the CIS Analyzer RGA CIS 70 and CIS 35 modes Do not modify those memory locations if you plan to use RGA Windows to control the CIS Analyzer The three sensitivity factors are measured at the factory for N2 9 28 amu and stored in units of
34. Procedure is to determine the voltages that the RF Driver must output at 0 and 128 amu so that all the peaks in an analog spectrum appear in the right position The RI command is used to program the voltage output of the RF Driver 0 amu during the Peak Position Tuning Procedure The value is saved in the non volatile memory of the CIS Head and used by the firmware to generate the internal scan parameters used to step the RF during scans and single mass measurements Note to Supervisors A calibration disable jumper JP100 available on the circuit board can be used by a supervisor to block any attempt to modify the value of the DI parameter Supervisors may use this feature to prevent accidental changes in the calibration parameters by inexperienced operators Setting JP100 will disable peak tuning of the CIS Head Parameters RIparam param 86 0000 86 0000 If Calibration is enabled by the JP100 jumper See CE Command the parameter is saved into the non volatile memory of the CIS Head and the internal scan parameters used to step the RF during scans and single mass measurements are updated accordingly RI Use this format to replace the peak tuning parameter with the original factory setting for the RF Driver output 9 0 amu The factory value is retrieved from memory and used as the new parameter value to excecute the command as above RI Query Returns over RS232 the parameter value currently saved in memory RI Uses the cur
35. RS232 ERR Byte Query Echo RS232 ERR Byte Query the value of the RS232 ERR byte The value of the RS232 ERR byte is sent to the computer in ASCII format and with a lt LF gt lt CR gt terminator RS232 ERR and bit 0 of STATUS are then cleared to provide a clean error reporting slate Important See Troubleshooting Tools in the Programming chapter for more details on the use of this query Parameters This command is a query and can only have one parameter format EC Error checking The only acceptable parameter is a question mark The absence of a parameter i e EC is treated as a bad parameter error Description DET ERR Byte Query Echo DET ERR Byte Query the value of DET ERR and update its value after running a fresh check on the Electrometer Bit5 of STATUS and the DET ERR byte are updated based on the tests results The DET ERR byte value is returned to the computer in ASCII format and with a lt LF gt lt CR gt terminator No errors are present as long as the byte value is zero Consult the Error Byte Definitions section in this chapter for detatils on the different error bytes of the CIS Analyzer Consult the Troubleshooting chapter of this manual for possible causes and solutions to any problems reported Always try the query a second time before declaring a hardware problem Important The electrometer is not affected by this test and the detector is restored to its pre test configuration once the comm
36. SRS Pe 24 voc s e voc s Grund Figure 2 ECU 24 VDC Power Connector RS232 cable A straight through RS232 cable with 9 pin type D connectors is needed to connect the IBM compatible PC to the ECU box An adapter will be needed if the RS232 port of the computer has a 25 pin Type D connector The probe must be installed in the vacuum chamber before the ECU box is mounted on its flange CIS Quadrupole Gas Analyzer 1 10 Installation Procedure 1 Begin by inspecting the front panel of the ECU box Use the following diagram as a reference during installation Probe alignment hales Clearance hales 6 places eadem 44 Brema rs SE SR PEU Pn on AH ONIN AA Internal connectors Locking screws f2 places Figure 3 ECU Front Panel 2 Next inspect the probe s feedthru flange Eight ceramic feedthru connectors on a 1 diameter circle surround a center tube terminated by a coaxial connector Two alignment rods 1 4 diameter insure the correct alignment of the ECU box to the probe during installation and two threaded holes 1 4 28 line up with the locking screws of the ECU box 3 Push the locking screws of the ECU box as far as they will go into the box 4 Orient the ECU so that the two probe alignment holes 1 4 diameter on its front panel and the alignment rods of the flange line up Note that there is only one correct way to do this 5 Slide the ECU into the probe using the alignment rod
37. STATUS error byte is the gateway to error diagnosis Important The CIS Analyzer is free of detected errors as long as the STATUS byte is clear no bits set Each bit of the STATUS byte reflects the result of a different type of internal check Each internal check involves several different tests on a component of the CIS Head See the Troubleshooting Chapter for details The results of the specific tests are stored in check specific error bytes All error bytes can be queried by the computer using the Error Reporting commands to find out which bits are set STATUS Bit Internal Check ERROR ono not used ao er 5 pe mom mm U 1 Ines Jm Jr s emus Teen e a Head component checked Each check involves several tests on the component b Internal checks automatically performed upon a power on reset c Error bytes that store the results of the tests for each type of internal check d The Error Reporting command that queries the error byte CIS Quadrupole Gas Analyzer Programming the CIS Head 5 25 The Error LED is immediately turned on if any one of the bits 1 7 of STATUS is set Bit 0 of STATUS reports communications errors and the Error LED is only flashed twice when the bit is set The STATUS Byte should be queried regularly by the programming software ER command Commands that involve hardware control such as Ionizer Control commands do diagnostic checks on the hardware as they are ex
38. Tuning Procedure eeeeeeeeee eene eene enne nnne nnne nne innen innen 6 14 CIS Quadrupole Gas Analyzer 6 2 Introduction Introduction Accurate qualitative and quantitative partial pressure measurements can only be assured by proper tuning of the CIS Head Correct calibration of the mass scale is essential during qualitative analysis for the correct assignment of mass numbers to the different peaks The mass resolution of the quadrupole mass filter Am oz must be kept at or under 1 amu to avoid severe overlap between adjacent peaks Changes in Am o during the measurements caused by aging severe contamination and large temperature changes will cause variations in the sensitivity of the instrument and the shapes of the fragmentation patterns of the molecules seriously affecting all quantitative measurements For careful quantitative analysis it is important that the sensitivity of the instrument be determined for every gas which may be a component of the system The sensitivity factors must be obtained under the same operating conditions that will be used during general partial pressure analysis since they depend on many instrumental parameters including ionization energy emission current mass filter setting type of detector etc For example the RGA CIS 70 and CIS 35 modes of operation will all have different sensitivity factors for the same gas since they correspond to three different sets of ioniz
39. a built in power supply Option 02 CIS Quadrupole Gas Analyzer 8 8 Basic Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause PS7 24VDC PIS External 24V P S error Voltage gt 26V Voltage output of 24VDC Power Supply exceeds the acceptable 22 26V DC range The Power LED is turned off and the Error LED is turned on instead Check the voltage output of the external power supply with a voltmeter Adjust the voltage to 24 V in adjustable external supplies or replace the power supply altogether if necessary Contact SRS for units with a built in power supply Option 02 RF4 Quadrupole Mass Filter RF P S RF P S Error Power Supply in current limited mode The circuit that drives the primary of the RF Transformer is in current limited mode Check for a short in the quadrupole connections of the probe Consult SRS if no obvious shorts are detected RF6 Quadrupole Mass Filter RF P S RF P S Error Primary Current exceeds 2 0 Amps The circuit that drives the primary of the RF Transformer is delivering an unusually large current Check for a short in the quadrupole connections of the probe Consult SRS if no obvious shorts are detected RF7 Quadrupole
40. a pump down to 10 Torr At this point the RGA may be used to check the quality of the background for leaks and contaminants Once the quality of the vacuum is satisfactory the sputtering chamber is backfilled with argon at a few mTorr and sputtering is started The low conductivity Lo C path is used when the process chamber is at pressures above 10 Torr This path contains a micro hole orifice which reduces the pressure several decades to a level suitable for the RGA typically around 10 Torr Apertures are available for operating pressures as large as 10 Torr For example during a sputtering process the RGA may be used to monitor water vapor and hydrocarbon levels to assure they do not exceed certain critical levels that degrade the quality of the sputtered films A pair of pumps draws the gas through the aperture to the RGA and establish the pressure drop The pumps are compact completely oil free and require minimal maintenance For pressures higher than 10 Torr the gas flow rates into the sample inlet side become extremely small and the time response is too slow for any practical measurements In those cases a bypass pumped sampling system with a much larger gass flow rate and faster response is a much better choice than a single stage PRGIS A commercially available example of a bypass pumped system is the QMS Gas Analyzer manufactured by Stanford Research Systems MDPP limitations of a PPR system with an OIS RGA An OIS RGA c
41. a very versatile intrument and can be used for a very large range of applications Different users will need to taylor this information to their specific needs For additional information on the subject of Partial Pressure Gas Analysis refer to 1 J Drinkwine and D Lichtman Partial Pressure Analyzers and Analysis AVS Monograph Series published by the Education Committee of the American Vacuum Society 2 Basford et al J Vac Sci Technol A 11 3 1993 A22 40 Recommended Practice for the Calibration of Mass Spectrometers for Partial Pressure Analysis Update to AVS Standard 2 3 For information on multiple linear regression analysis consult 1 William H Press et al 1992 Numerical Recipes in C The Art of Scientific Computing Second Edition Cambridge Univ Press section 15 4 page 671 2 Bevington P R 1969 Data Reduction and Error Analysis for the Physical Sciences New York McGraw Hill Chapters 8 9 How Mass Spectra are Interpreted A mass spectrum taken in a real system will almost always contain signals from a mixture of various gases Careful and complete interpretation of the spectrum i e a complete spectral analysis should reveal the identity as well as the concentrations of the various components which have produced the spectrum The first step in the spectral analysis process is to correctly identify the mass to charge ratio of all the peaks in the mass spectrum A well calibrated mass scale is
42. accuracy of the ion current measurements is insured by an internal calibration procedure that calibrates the output of the electrometer against input current over its entire operating range The I V response can be recalibrated at any time with the CL command The bandwidth and detection limit of the electrometer are programmed with the NF Noise Floor command A decrease in the Noise Floor setting results in longer measurement times with cleaner baselines and lower detection limits Histogram scans analog scans and single mass measurements share the same NF setting The CIS Head automatically adjusts the scanning rate and averaging based on the NF setting selected Important The zero of the ion detector is automatically readjusted at the beginning of each analog and histogram scan so that the baseline is always centered around zero The zero can also be readjusted at any time with the command CA In both zeroing procedures the output of the electrometer is measured in the absence of input ion current and stored as a current value in the spectrometer s memory The current value called offset correction factor is then automatically used by the firmware to offset correct all ion currents measured i e including those from single mass measurements under the same detector settings The detector settings are the electrometer s noise floor parameter value and the type of detector i e FC or CDEM in use at the time the zeroing is performed O
43. analyzer chamber into the ionization region The entire ionizer is made out of gold plated SS304 Gold plating serves several purposes It reduces the background levels in the ionization region Gold is very inert and does not adsorb species as readily as stainless steel does This results in reduced outgassing and electron stimulated desorption ESD Gold is also a very good IR reflector and reflects the radiation emitted by the filament back into the analyzer chamber As a result the ionizer walls run cooler and outgas less than with almost any other wall material Jtimproves the long term stability of the instrument Surface contamination in the ionizer is one of the leading causes of performance degradation and filament failure in quadrupole gas analyzers Gold is very inert and does not interact with many of the species that are present in modern day processes It lets the ionizer be exposed to many reactive and corrosive gases that would otherwise react with the wall materials The ionizer is fitted with a straight Tungsten W filament ThO Ir is only offered as an option The straight filament wire is positioned in close proximity to the emission slit The electrons are very efficiently directed into the slit by a negatively biased repeller plate mounted behind the wire Tungsten material is the preferred choice for process monitoring in the semiconductor industry because it minimizes chemical reactions reducing background
44. and automatically updates the Peak Tuning Parameters in the CIS Head based on the results of the calibration The overall adjustment procedure is very simple and must follow the steps described below 1 Low mass peak position adjustment 2 High mass peak position adjustment 3 Repeat 1 amp 2 in that order one or two more times until no more changes in peak positions are observed 4 Low mass resolution adjustment High mass resolution adjustment 6 Repeat 4 amp 5 in that order until no more changes in peak width are observed CIS Quadrupole Gas Analyzer 6 6 Peak 4 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 Tuning Procedure 7 Repeat amp 2 in that order one or two more times in the case steps 4 amp 5 caused changes in peak positions Important Collect a fresh analog scan for each step The peak positions are adjusted such that all peaks throughout the scanning range of the CIS Analyzer fall within 0 25 amu of their known mass to charge ratio This is required to make sure that the Peak locking algorithm used for single mass measurements always finds the mass peak within its search window The peak width Amjox must be a constant and less than 1 amu throughout the whole scan range Example The following figure shows the result of peak tuning the CIS Analyzer based on the H O low mass 18 amu and Za high mass 86 amu calibration peaks All peaks are at their correct mass settings and show absolute r
45. as Peak Position and Peak Width Tuning respectively Note A mixture of He Ar Kr and Xe inert gases is used at SRS to Peak Tune the CIS Analyzers The resolution is adjusted to 1 amu and peak tuning parameters are saved into the CIS Head before shipping The inert gases cover a broad mass range and they do not interact with the CIS probe i e they do not contribute to its aging Perfluorotributylamine is commonly added to the calibration gas to test the mass axis calibration above 200 amu in CIS300 units Peak tuning can be easily performed with RGA Windows using the Peak Tuning command of the Head Menu The program provides password protection for locking out the Peak Tuning Parameters so that casual users cannot alter the mass scale calibration or the spectrometer s resolution CIS Quadrupole Gas Analyzer Peak Tuning Procedure 6 5 An extra copy of the tuning parameters determined at the factory for the mass filter is saved in the CIS Head before shipping and those values can be retrieved at any time in case they are necessary Consult the RGA Windows User s Manual or the On line Help Files included with the program for details Note to Supervisors A calibration disable jumper JP100 can be configured to block any attempt to change the value of the mass filter settings in the CIS Head The jumper is located on the top electronics board of the ECU box next to the microprocessor chip i e biggest component on the board and its two
46. available quadrupole mass spectrometers is not part of this detection setup since the large aspect ratio length to diameter of the FC assures efficient recapture of secondary electrons The electron multiplier is a state of the art Macro Multi Channel Continuous Dynode Electron Multiplier CDEM It consists of a straight four channel tube made out of a special resistive glass i e high secondary electron emission yield with a cone of the same material attached to the front end It is placed upright next to the FC and away from the axis of the analyzer off axis configuration It is held safely in position by a clamp and a clip The clamp is connected to the neighboring rod that carries the voltage from the High Voltage power supply and is responsible for biasing the cone as well as assuring its correct placement next to the FC A hole on the side of the FC Shield allows space for mounting the CDEM cone very close to the top of the FC The clip CIS Quadrupole Gas Analyzer 3 16 lon Detector anchors the CDEM glass tube to the side of the FC Shield and holds the lower end of the tube at ground Chrome electrical coatings deposited at both ends of the tube provide the necessary electrical contacts A plate CDEM Anode mounted at the exit of the CDEM collects the secondary electrons The resulting electron current flows into the electrometer through a separate feedthru of the flange The entire setup is self aligning and easily service
47. centered on the exit plate Direct sampling provides good sensitivity due to the large ion densities available and also fast response times The memory effects typically associated to pressure reduction and conductance orifices are significantly reduced Improved Signal to background ratios Because the sampling pressure in the CIS is typically two decades higher than that of the rest of the sensor s vacuum system the signal to background ratio is significantly increased relative to the OIS PPR systems This is particularly important when measuring common residual gases such as water In order to best illustrate this point we go back to the example of a 10 Torr Ar sputtering process The sampling orifice in the OIS PPR inlet system reduced the Ar partial pressure from 10 down to 10 Torr at the OIS Water vapor levels were measured in a background of at least 10 Torr of residual water This corresponded to a 100 PPM MDPP limit for water Things are much better in the CIS system In this case the Ar gas is ionized directly at 10 Torr i e three orders of magnitude higher than in the OIS PPR but in the same background 10 Torr of residual water This residual level now corresponds to a 100 PPB MDPP level for water in the CIS system This is quite an improvement over the OIS PPR performance The combination of direct sampling and differential pumping provides the potential for PPM and sub PPM detection limits for even the most per
48. chamber Hydrogen water and nitrogen recover their original values but slowly The oil is alarming because it persists at a higher concentration If this sequence occurred several more times the oil would continue to increase The RGA allows it to be detected before reaching undesirable levels Table Mode The noise floor of the Faraday cup detector is about 10 mbar Since the maximum operating pressure is 10 mbar the dynamic range of the RGA is 6 decades or 1 ppm The noise floor of the channel electron multiplier CEM is lower but its maximum operating pressure also decreases with the noise floor The two pressure limits change such that the dynamic range of the CEM is still 6 decades By switching between the two detectors measurements covering more than 6 decades can be made The table mode of the SRS RGA software allows such a measurement to be made The CEM status can be set independently for each mass being monitored Figure 5 shows a configuration where the prevalent gases are detected with the FC and the low pressure gases are detected with the CEM A comparison of the value for nitrogen and floor show that the apparent dynamic range is 8 decades or 10 ppb The program will automatically sort the channels so that all the measurements requiring the CEM are made as a group which minimizes the switching on and off of the detector Without the ability to choose between FC and CEM detector for each channel the CEM would have to be used
49. complement format and Least significant byte first The detector settings i e detector type and electrometer s noise floor setting to be used during the scans must be selected in advance with the NF and HV commands The zero of the ion detector is automatically readjusted at the beginning of each analog scan so that the baseline is always centered around zero The offset correction factor calculated and stored in memory will then be used to correct all currents measured under the same detector settings The internal scan parameters used by the firmware to step the RF during the scan are checked and corrected at the beginning of the scan to make sure that the correct RF levels i e as specified by the last Peak Tuning procedure are programmed on the RF rods as a function of mass CIS Quadrupole Gas Analyzer 5 16 Programming the CIS Head Important An extra current value in addition to the values corresponding to the mass steps is sent at the end of all analog and histogram scans This extra current value is unrelated to the scan and does not need to be saved or displayed however it must be taken into account whenever analog scanning is incorporated into custom software The detector s zero and the internal scan parameters are checked and corrected at the beginning of each scan resulting in a slight delay before the scan actually starts The measurements are performed with the detector setting that is active at the time the sc
50. deeg gedeien giee 9 12 Filament Heater Supply 2 1 erede HE eee e Ere cea 9 12 Bias Regulators eeschte ee tee e tee dee 9 13 Schematic name ONSE B3 4 uleeeeeeeiieseseesnee seen nnne nasa nnns rasa ansa ennn nenn saa a s Da sa sa sr Ds sa sa snc 9 14 Power Supplies tede eren E esee tede eri te PP ee 9 14 Schematic name QMSE V1 uui adiiedd aaiien nnne nanne nanne ennn nnmnnn nnmnnn nnmnnn na 9 14 CIS Quadrupole Gas Analyzer X Contents Signal Conditioning EE 9 14 Schematic name QMSE V2 EE 9 16 Electron Multiplier High Voltage Power Supply eee 9 16 Chapter 10 Probe Assembly 10 1 CIS Quadrupole Probe Assembly Schematic eeeeeseeeeeeesiees esee enne nein SEENEN REENEN 10 3 CIS lonizer Exploded Schematic esee eeseeee einen ens nnne nnn nn nhan tasa sna natn nns 10 4 Feedthru Flange Connectors Schematic essei eeeeeees esses eene nennt innata natn nnn 10 5 Appendix A Vacuum Diagnosis with SRS RGA s Appendix B Using SRS RGA s to Sample High Pressure Gasses Appendix C SRS RGA Output Control Options O100TR and O100TS Appendix D PPM Level Gas Analysis The Closed lon Source CIS Advantage Glossary of Terms References Specifications xi Specifications Operational Mass Range CIS100 to 100 amu CIS200 to 200 amu CIS300 1 to 300 amu Ion Source High Conductance Closed Ion Source CIS Mass filter typ
51. depending on the state of the DE GAS bit to the voltage seen on CIS Quadrupole Gas Analyzer Description of Schematics 9 13 the 100Q emission current shunt resistor R522 The current sensed by this resistor is actually composed of three components the filament emission current the repeller voltage 100kQ and Vref 5V 30kQ All of these components sum With a repeller voltage of 60V the two non emission sources sum to 0 60 0 166 0 766 mA So to set an emission current of 2 mA EMIT SET which provides 1 mA V is set to 2 766VDC The emission current may be set to values as high as 50 mA during the de gas procedure The primary side current drive may be sensed in the 0 5Q FET source resistor The voltage across this resistor is filtered and amplified by 6X and may be measured by the CPU The duty cycle of the FET switches may also be measured by the CPU via the voltage labeled FIL DUTY A drop of about 40 in the primary side current for a particular duty cycle value indicates that one of the two parallel filaments has burnt out A drop of 90 indicates that both filaments are missing If the source sense resistor voltage reaches 1V when the primary side current reaches an instantaneous value of 2A the LT3525 will terminate the gate drive to FET for the remainder of the cycle This feature protects the circuit in the case of a short circuit or other severe fault Bias Regulators The regulated repeller and focus plate biase
52. detected queering the contents of the STATUS byte in the CIS head The query command ER returns the value of the STATUS Byte for analysis and a communication error is present if Bit 0 of STATUS is set The specific problem is determined querying the bits of RS232 ERR byte with EC which clears the RS232 ERR byte and Bit 0 of STATUS at the end of its execution to provide a clean error reporting slate Communication errors accumulate in the RS232 ERR byte as they occur and the byte can only be cleared with the EC Command or turning off the instrument Note Please refer to the Error Byte Definitions section of this chapter for a complete listing of the error and status bytes of the CIS Analyzer Also consult the Error Reporting Commands list for details on the EC and ER commands CIS Quadrupole Gas Analyzer Programming the CIS Head 5 11 Programming the CIS Head This section describes the basic programming steps needed to configure operate and diagnose the CIS Analyzer The emphasis is on general program implementation without going into specific details on the different commands that are mentioned Please consult the CIS Command Set section of this chapter to get more detailed information on the spectrometer s commands and their implementation Initializing the CIS Head The CIS Head is ready to communicate a few seconds after it is turned on right after all the built in internal checks are performed The Initialization co
53. essential to this task See the Tuning Chapter of this manual for a detailed description of the mass scale calibration procedure Once all the peaks have been labeled the next step is to identify the residual gases that have produced the spectrum Knowledge of your process or the recent history of your system may provide very valuable clues as to the possible gases that may be present in the vacuum chamber A familiarity with the standard spectra of commonly expected gases will generally help to determine the major and minor components in the system Any peak in the spectrum may consist of contributions from molecular ions and or fragment ions or multiply ionized CIS Quadrupole Gas Analyzer Partial Pressure Analysis Basics 2 13 species The qualitative spectral analysis is completed when all the peaks in the spectrum have been uniquely assigned to the components of a gas mixture in complete agreement with the known fragmentation patterns of the components In cases where only the major components are of interest some of the minor peaks of the spectrum will remain unassigned If only a few species are being monitored only the peaks corresponding to the substances of interest need to be assigned and monitored Notes on Fragmentation Patterns The electron impact type of ionizer used in modern quadrupole mass spectrometers almost always causes more than one kind of ion to be produced from a single type of gas molecule Multiple ionizat
54. for all channels so that the low pressure gases could be detected Operation like this would cause the CEM detector to saturate at the high pressure peaks Saturation of the detector makes the value useless and also increases the physical wear on the CEM SRS Residual Gas Analyzer Appendix A 11 toe 5o 1 Kee ve LL Cen L TFIIH LEE HK OFF OFF OFF On On On On AE Figure 5 SRS RGA Table Display Leak Testing In addition to the diagnosis of vacuum systems the RGA is invaluable as an intrinsic leak detector It is always available and does not require perturbing the system The user does not have to roll up a large leak detector and attach it to the vacuum system The system does not have to be brought up to atmospheric pressure The RGA can operate in leak detection mode using any gas so it does not require helium For moderate leaks argon or tetrafluoroethane a typical gas in cans of dust off can be used Helium is necessary for only the smallest leaks Having a built in leak detector makes working with vacuum systems much easier and faster and the SRS RGA is far less expensive than a standard helium leak detector The process of leak detection with an RGA is the same as with a traditional helium leak detector Place the software in leak detection mode indicate the mass of the test gas and watch the partial pressure as various joints in the vacuum system are sprayed with the test gas When the leak is sprayed with
55. for the CIS Analyzer Its two main advantages are a faster scan rate than analog scans and a reduced amount of data being exchanged during the scan The CIS Analyzer as a Single Gas monitor The CIS Analyzer can measure individual peak heights at any integer mass within its mass range This mode of operation is used to generate data for leak testing measurements and to track changes in the concentrations of several different components of a mixture as a function of time The outputs provided by a set of single mass measurements are often used in process control programs to control alarms analog and digital outputs and relays RGA Windows uses this mode to generate its data for the Table Pressure vs time Annunciator and Leak Detection modes Peak Locking procedure During a Single Mass Measurement the CIS Analyzer performs a Miniscan around the mass requested and the maximum current value measured is sent out over RS232 The scanning procedure referred to as Peak Locking is designed to measure peak currents for individual masses in a mass spectrum without being affected by drifts in the mass axis calibration The Miniscan covers a 0 6 amu range centered at the mass requested and selects the maximum current from 7 individual measurements performed at 0 1 amu mass increments CIS Quadrupole Gas Analyzer 2 8 Basic Operating Modes Basic Operating Modes The low detection limits together with the wide dynamic range provided by the
56. have a fused Power Entry Module with a built in power switch PA Locking knob HSea3e connector LEDs Power connector Cooling fan hpt voltage E set autom stics ly Leea line wokage and Lesen within ranges at right Input volage 90 264 VAC ds Input Frequency 47 63 Hz Buit in power module option 02 Figure 3 ECU Rear Panel 24VDC 2 5A Connector Use this connector to provide external power to the CIS Analyzer The ECU electronics must be powered with a 24 V 2V DC power supply 2 5Amps The power supply must have a cable with a 9 pin type D female connector on the free end wired as described in the ECU 24VDC power connector diagram shown below CIS Quadrupole Gas Analyzer 4 6 Rear Panel 1 sesvoc e se voc s se voc s Gros Figure 4 ECU 24 VDC Power Connector RS232 DCE 28 8k Connector LED s Use this connector to interface the CIS Analyzer to a computer The RS232 interface connector of the CIS Analyzer is configured as a DCE transmit on pin 3 receive on pin 2 with full RTS CTS handshaking enabled Use a straight through RS232 cable with 9 pin type D connectors to connect the computer usually DTE to the ECU The communication parameters are fixed at 28 800 baud rate 8 data bits no parity 2 stop bits Eight LED s provide constant feedback on the operation of the CIS Head The function of the LED s is described later in this chapter Locking Knobs Use t
57. in the ionizer The electrons are accelerated into the anode grid where the ionization of the gas molecules occurs Electron emission current The electron current from the filament to the grid in mAmps Ion current signals scale linearly with the electron emission current Note The available emission current range in the SRS RGA is 0 to 3 5 mA Electron Energy The kinetic energy of the electrons in eV used for electron bombardment in the ionizer Note In the SRS RGA the Electron Energy is equal to the voltage difference in Volts beween the filament and the anode grid Electronics Control Unit abbreviation ECU Electronics box that attaches directly to the probes feedtrhu flange and contains all the necessary components to operate the quadrupole mass spectrometer and communicate with a host computer Faraday Cup A charged particle detector consisting of a metal electrode for the direct collection and detection of charged particles Note Typical designs are cup shaped to minimize secondary electron losses Filament Ionizer Component The source of the ionizing electrons Thin thoria coated Iridium wire that operates at a negative potential relative to ground and is resistively heated to incandescence with an electrical current from the emission regulator The thermionically emitted electrons are accelerated towards the anode grid which is positively charged with reference to the filament and ground Focus Plate Ionizer com
58. is simply stored so it can be read and CIS Quadrupole Gas Analyzer Parameter Storage Commands 5 51 used by a host computer For example RGA Windows uses the High Voltage value returned by MV to set the bias voltage in the CDEM As expected this command is only available in heads with a CDEM option installed See MO command for details Parameters MVparam param 0 2490 The parameter interpreted as a CDEM bias voltage in units of Volts is stored in the non volatile memory of the head MV CDEM Bias voltage query Error checking The absence of a parameter i e MV is treated as an error No default value is available A bad command communications error is reported when this command is invoked in a unit with no CDEM option installed XAparam param 0 10 Description Parameter Address Echo Query Response Select a specific element within the Parameter Storage Table A Parameter Storage Table capable of storing up to 10 different numeric values i e elements is part of the non volatile memory of the CIS Head The command pair XA XV is used to update or query the elements of that table XA where A is for Address is used first to point at any one element within the table XV where V is for Value can then be used to query or update the value of the element previously pointed to by XA The numeric storage available through XA and XV is often used to store a variety of instrument specific calibration data d
59. is treated as a bad parameter error Bit3 of STATUS transmitted at the end of the command reports errors in the excecution of the command CEM ERR byte must be consulted to find out the specific problem encountered See EM in Error Reporting command list Description Electron Multiplier Option Query Echo Query Response Query the electron multiplier CDEM option in the CIS Head being programmed The CIS Analyzer is provided standard with a Faraday Cup detector For increased sensitivity and faster scan rates an optional CDEM is offered The MO command can be used to determine whether Electron Multiplier detection is an option in the CIS Analyzer being programmed Note See also EM command in the Error Reporting commands list for an alternative way to query the CDEM option Parameters Query is the only possible format MO The value returned over RS232 in ASCII format has two possible values 0 lt LF gt lt CR gt No CDEM option is available 1 lt LF gt lt CR gt CDEM option is available Error checking Command must have a query format or a bad parameter error is reported NFparam param 0 7 Description Electrometer s Noise floor setting Echo Query Response Set the rate and detection limit for ion current measurements A decrease in the Noise Floor setting results in cleaner baselines and lower detection limits during scans and measurements but also means longer measurement and scanning times
60. logarithmic output of the picoammeter is not within the levels expected for a 5 nA input current Contact SRS CIS Quadrupole Gas Analyzer 8 6 Basic Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting DET6 Electrometer Electrometer Error DETECT fails to read 5nA input current The logarithmic output of the picoammeter is not within the levels expected for a 5 nA input current Contact SRS DET7 Electrometer Electrometer Error ADC16 Test Failure The 16 bit analog to digital converter used to digitize the logarithmic output of the picoammeter reports an output greater than 15 mV when its input is grounded Contact SRS EM7 Electron Multiplier Electron Multiplier Error No Electron Multiplier Option available in this head A function involving the electron multiplier was invoked in a unit that does not include the CDEM option Option 01 Do not use any of the CDEM related commands in this unit Upgrade to an Electron Multiplier option Option 01 FL6 Filament Background Protection Mode Filament Error Unable to set the requested emission current The filament heater was unable to establish the requested emission curren
61. low and high mass peaks show up at their known positions Peak Width Tuning Algorithms Constant absolute resolution mue in a quadrupole mass filter requires DC voltages linearly related to the mass with a slight negative offset at low masses i e negative intercept The CIS Head dynamically adjusts the DC levels of the quadrupole filter during measurements so that constant mass resolution is automatically available throughout the entire mass range of the spectrometer The bulk of the DC voltage is supplied by a DC power supply whose output is linearly related to the RF amplitude The rest of the DC voltage DC_Tweek is provided by the output of an 8 bit digital to analog converter DAC The firmware uses two Peak Tuning Parameters DI Intercept and DS Slope stored in the non volatile memory of the CIS Head to calculate the 8 bit settings of the DAC according to the linear equation DACH m DS m DI DC Tweek m DAC8 m 128 19 6 mV where m is the mass in amu and DAC8 m is the 8 bit setting at that mass The purpose of the Peak Width Tuning Procedure is to determine the values of DI and DS so that all the peaks in an analog spectrum have the desired peak width typically Am 4 21 amu The calibrated parameters are saved in the non volatile memory of the CIS Head DI and DS commands respectively and used by the firmware to generate the internal scan parameters used to adjust DC Tweek during scans and single mass mea
62. mass measurements and scans and detectable partial pressures better than IO TT Torr during electron multiplier detection The instrument is completed with the RGA Windows software package that runs on IBM compatible PC s 486 or greater The intuitive graphical user interface allows measurements to be made and displayed in a variety of modes The program is fully interactive and measurements are set up quickly and easily with the click of a mouse The software also supports multiple head operation when more than one CIS head is needed Please refer to the RGA Windows chapter of this manual and the RGA On Line Help files provided with the program disks for detailed information on the features procedures and commands available in the RGA Windows program Intelligent firmware built into the CIS Head completely controls the operation of the instrument and provides the three basic modes of data acquisition of the mass spectrometer e Analog scanning e Histogram scanning e Single mass measurement RGA Windows provides fast access to all the CIS Analyzer functions and modes of operation without the need for any computer programming however the instrument can also be programmed directly using the CIS Command Set supported by its serial interface Consult the Programming chapter of this manual for information on the programming options and a complete listing of the CIS Command Set CIS Quadrupole Gas Analyzer 2 4 The SRS Closed lon S
63. modern day contamination control requirements for gas phase processes are constantly pushing the limits of performance of quadrupole gas analyzers The technology is rapidly evolving and adapting to lower contamination level specifications A good understanding of the different factors affecting the detection limits of the different gas analysis systems currently available is an essential tool while selecting a sensor for a specific application As it is usually the case most choices involve compromises and a good understanding of the basic tradeoffs will minimize mistakes and maximize productivity A well matched gas analyzer rapidly becomes an integral part of the processing system and its information eliminates most of the guesswork that is part of all troubleshooting procedures The main purpose of this application note was to introduce the basic concepts required to choose the best gas analyzer for any practical application and also to present some of the basic operating principles that must be kept in mind to assure the optimum performance of the instrument selected All gas phase processing setups can benefit from the addition of a quadrupole gas analyzer Miniaturization smart software interface and improved detection limits are some of the features to look for in future instruments As sensors become more affordable they will rapidly become commonplace in all industries requiring the strict control of contamination levels in process gas
64. number returned by the AP query Parameters This command is a query and can only have one parameter format AP Error checking The only acceptable parameter is a question mark The absence of a parameter i e AP is treated as an error Description Histogram Scan Points Query Echo Query Response Query the number of ion currents that will be measured and transmitted during a histogram scan under the current scan conditions Important The query response does not include the extra current 4 bytes that is transmitted at the end of all histogram scans Please see HS command for details CIS Quadrupole Gas Analyzer Scan and Measurement Commands 5 41 The number of points ion currents retuned over RS232 is calculated based on the MI and MF parameter values Number of points MF MI 1 Each point transmitted represents an ion current and as such corresponds to 4 bytes being received by the host computer The HP query is used to verify that the CIS Head and the host computer agree on the number of bytes that will be exchanged over RS232 during the histogram scan The total number of bytes sent out to the host computer during an histogram scan is obtained multiplying by four the number returned by the HP query Parameters This command is a query and can only have one parameter format HP Error checking The only acceptable parameter is a question mark The absence of a parameter i e HP is treated as a Ba
65. ordered directly from Stanford Research Systems Consult the High Pressure Sampling section in the General Operation chapter of this manual for more information on this subject Read the General Operation chapter of this manual for an overview of the instrument and its functions Take a moment at this time to read the CDEM Handling and Care section of the Maintenance chapter if your unit includes the electron multiplier option Option 01 Do not power up the instrument until it is instructed in the installation procedure Inspect all components of the SRS CIS Analyzer upon unpacking Report any damage to Stanford Research Systems immediately Compare the contents of the shipping container with the Checklist below and report any discrepancies Standard Equipment Supplies l 2 One CIS Probe with plastic plugs sealing vacuum ports One Electronics Control Unit box CIS Quadrupole Gas Analyzer SR 6 Unpacking 1 3 Two 3 5 inch floppy disks with RGA Windows software DB9 DB9 RS232 cable 25 length DB25 to DB9 connector adapter Operating Manual and Programming Reference Accessories 1 Female DB 9 cable connector with two wires for 24V power supply connection not provided with Option 02 Optional Equipment 1 2 10 11 12 Option 01 Electron multiplier with HVPS Preinstalled at the factory Option 02 Built in power module for AC line operation Preinstalled at the factory Includ
66. plate may collect ions when set to any potential below the grid potential and since it may collect electrons when set to any potential above the repeller voltage the focus plate regulator is designed to sink or source current CIS Quadrupole Gas Analyzer 9 14 Description of Schematics The grid voltage is supplied by the op amp U502A This op amp is operated with a gain of six to amplify the voltage selected by the analog switch U500 The op amp is protected from possible discharges which would connect the grid to the repeller potential by R517 and D500 For a high power de gas a DPDT relay is used to by pass the bias regulators connecting the grid and repeller directly to the un regulated 250Vdc and 150Vdc supplies During de gas the filament emission current is set to 20 mA which will provide about 8W of power to heat the grid in addition to 15W of filament heater power Schematic name QMSE B3 Power Supplies The unit is operated from 24VDC and requires up to 2 0A The current draw will be the highest when the unit is scanning at the high end of the mass range or during de gas The unit is protected against power supply reversal by D610 A 5A circuit board mounted fuse limits damage in the case of a severe circuit failure The DC input is filtered by C615 L601 and C616 which also reduce conducted emissions from the unit A DC DC inverter is operated from the 24V supply to provide 140V for the repeller 250V for the mas
67. query The number 50 is echoed Add one for extra current that is not displayed HS1 Histogram Scan trigger 1 scan is collected and transmitted Histogram Scan Programming Tips It is good programming practice to follow each command that sets a parameter with a query of the parameter setting For example the first command in the list should be followed by a MI and a number 1 should be echoed by the CIS Head Notice that MI and MF are shared by analog and histogram scans Any command sent to the CIS Analyzer during scanning will immediately halt the scanning action and clear the transmit buffer Remember to also clear the computer s receive buffer to reset the communications The command responsible for stopping the scan is executed It is good practice to perform an analog scan before triggering a large set of histograms to assure the correct peak tuning i e correct peak locations and widths of the quadrupole mass filter Perform a complete Peak Tuning Procedure as described in the Tuning chapter of this manual if significant shifts in the peak locations are observed The CIS Analyzer has the ability to store a complete scan in its output buffer The scan remains in memory until all the data is transmitted out to the host computer over RS232 As a result of the high acquisition rate there might be a delay between the time at which the data is collected and the time at which a complete spectrum is displayed by the host computer The ti
68. remain unafected If the filament is off the new electron energy setting is stored in memory for the next time the filament s emission is activated Command excecution times vary depending on the pre existing ionizer conditions The end of the command excecution is prompted to the host computer by sending out the STATUS byte over RS232 Note The Electron Impact Ionization Energy is set to the default value when the unit is turned on Important The repeller plate and the extraction plate are only biased while the filament is emitting electrons Parameters EEparam param 15 105 The parameter represents the electron impact ionization energy in eV EE The default Electron Energy value is used to run the command Default 70 eV EE Query The electron energy parameter setting is returned over RS232 in ASCII format Error checking Number parameters must be within the accepted range and must be integers The absence of a parameter i e EE is treated as a parameter error FLparam param 0 00 3 50 Description Electron emission current mA Echo STATUS error byte or query response Set the electron emission current level in the ionizer The parameter represents the desired electron emission current in units of mA CIS Quadrupole Gas Analyzer lonizer Control Commands 5 31 When a finite emission current is requested the CIS Head biases the ionizer s repeller and extraction plates and activates the
69. settings are clearly indicated as CAL DIS and CAL EN Supervisors may use this feature to prevent accidental changes in the calibration parameters by inexperienced operators Peak tuning is completely disabled when the jumper is configured to the CAL DIS setting Tip Virtually every vacuum system will have detectable amounts of hydrogen 2 amu water 18 amu carbon monoxide 28 amu and carbon dioxide 44 amu Become familiar with these species and their fragmentation patterns and use their peaks to quickly check the correct performance of the instrument i e mass scale calibration and mass resolution while operating the instrument General Procedure Peak tuning is a simple procedure that requires the introduction of two known gases into the vacuum system A low mass gas 1 20 amu recommended is used to adjust the low end of the mass axis a high mass gas with a mass to charge ratio close to the upper limit of the instrument s mass range is used to adjust the high end of the mass scale Several analog scans are performed on the sample and the peak positions and widths are checked and adjusted as necessary Changes in resolution affect the sensitivity of the analyzer and a Sensistivity tuning procedure should always be performed at the end of the peak tuning process The entire procedure can be carried out with the help of the Peak Tuning command Head Menu of RGA Windows The program guides the user through the calibration procedure
70. some are listed at the end of this note SRS Residual Gas Analyzer 2 Appendix B Figure 1 Schematic of a mid vacuum pressure reduction system Apertures can be readily designed for process pressures in the range from 10 mbar to 10 mbar If the process always operates within a small range the aperture can be optimized to deliver gas to the RGA at about 10 to 10 mbar By operating the RGA at its optimum pressure the data acquisition time is kept to a minimum and the full dynamic range in partial pressure is available For many applications the process is operated at one pressure and the aperture can be optimized If the process pressure varies over a range of 2 decades or more the aperture size must be compromised to tolerate the pressure range For example consider a process pressure that varies from 10 to 10 mbar The aperture would be designed to drop the pressure from 10 mbar to 10 mbar When the process pressure was at 10 mbar the pressure at the RGA would be 10 mbar The minimum detectable partial pressure MDPP of the RGA does not depend on the operating pressure for a Faraday cup detector it is about 10 mbar Therefore the dynamic range of the measurement varies from 5 decades at high process pressure to only 3 decades at the low pressures For applications where the full dynamic range is not needed operating the RGA at low pressure may be acceptable If the full dynamic range is required over a variety of process p
71. the ionizer and fix any shorts Note Use the information in the Maintenance chapter to remove the repeller and or service the ionizer If no short is detected the filament might be damaged or worn out Inspect the filament best with a magnifying glass and look for damage or contamination on the wire If a problem is suspected replace the filament using the procedure in the Maintenance chapter If the filament still does not turn on contact SRS FL7 Filament Background Protection Mode Filament Error No filament detected No filament was detected after an attempt was made to establish emission current in the ionizer The Error and Burnt LED s are turned on by this error A probe must be connected to the ECU The probe must have a filament The filament must be intact Use an ohmmeter to check continuity across the filament The two filament feedthrus can be easily identified using the drawings in the Probe Assembly Chapter The probe must be correctly connected to the ECU Tighten the locking screws of the box PS6 24VDC PIS External 24V P S error voltage lt 22V Voltage output of 24VDC Power Supply is under the acceptable 22 26V DC range The Power LED is turned off and the Error LED is turned on instead Check the voltage output of the external power supply with a voltmeter Adjust the voltage to 24 V in adjustable external supplies or replace the power supply altogether if necessary Contact SRS if your unit has
72. the Auto Scale button or selecting Auto Scale from the Graph Menu e Change the Y Axis to a logarithmic scale selecting the Log option of Select Scale in the Graph menu item Please refer to the RGA Windows User s Manual and the RGA On Line Help files provided with the program disks for detailed information on all the features procedures and commands available in the RGA Windows program Read the General Operation chapter of this manual for a general overview of the SRS CIS Analyzer and its basic operating modes Consult Appendix D for information on the application of the CIS Gas Analyzer to PPM Level Gas Analysis CIS Quadrupole Gas Analyzer Chapter 2 General Operation This chapter describes the basic properties and operating modes of the Stanford Research Systems CIS Quadrupole Gas Analyzer CIS Analyzer In This Chapter The SRS Closed lon Source Quadrupole Gas Analyzer eese entente 2 2 Basic Data Acquisition Modes essei seien eeee eene entnehmen nnne nn nnns nennen innen r anseres 2 5 Principles of operation 5 EES 2 5 The CIS Analyzer as a Mass spectrometer eeeeeeesiseeseseee nennen nennen nn nnne nn nna 2 6 The CIS Analyzer as a Single Gas monitor eeeieeeseeeeeeees esee nennen nennt 2 7 Basic Operating Modes nc hnic eegene EE 2 8 RGA Mode UHV lt P lt 10 CT eerte tette tette testa
73. the desired emission current and let the electronics warm up for at least 15 minutes Once the warm up time has elapsed try to operate the analyzer to see if the problem has disappeared for example trigger a scan over a large mass range If the problem is still present warm up the unit further by setting the quadrupole mass filter to 250 amu for 15 minutes see Programming the Quadrupole Mass Filter in the Programming chapter of the manual It is good practice to keep the filament on as long as the instrument is turned on ans safe operating pressures are present Operating the filament keeps the electronics and the probe completely warmed up and assures reproducible readings at all times The filament is burn out resistant and will operate continuously for a long time Note During the warm up period RGA Windows users should see that the mass range over which the instrument can be operated reliably increases with time until it goes beyond the user s requested scan range No more warnings are posted beyond that point If no improvement in the mass range is seen as the unit warms up then go on with the troubleshooting procedure e Is the probe correctly connected to the ECU box Try disconnecting and reconnecting the ECU box to the probe Securely tighten the thumb screws to make sure good contact is made between the RF P S and the quadrupole rod pairs I none of the above steps solves the problem consult SRS or your local representative f
74. the end of the probe and slide the entire quadrupole assembly out of the vacuum tube The ionizer the filter and the detector are now fully exposed and easily accessible The alumina seal SRS 7 00787 remains attached to the CIS Port held in place by a c clip CIS Mounting Flange Feedthru Flange Process Chamber CIS Cover Tee onizer Vacuum a Probe Assembly E Pumping System 222575557 Figure 5 Probe Removal for Quadrupole Filter Cleaning 6 Carry the probe to a clean dust free area immediately Avoid contamination using handling procedures compatible with high vacuum requirements 7 Hold the probe in a secure upright position and do a thorough visual inspection of the unit Check for loose damaged misaligned and severely contaminated components If excessive contamination is evident take the necessary steps to identify and eliminate the contamination sources in the vacuum system Carefully inspect the ionizer and if any problems are detected replace the filament and or the ionizer as part of this maintenance procedure Inspect the CDEM for signs of arcing and contamination If necessary replace the CDEM as part of this maintenance procedure 8 Head disassembly Only a rough outline of the complete disassembly of the probe is presented here Use the Assembly Drawings in the Probe Assembly chapter of this manual as a visual aid during the process
75. the filament quadrupole and detector Oil free turbo pump based stations compatible with the CIS Analyzer are available directly from Stanford Research Systems see for example Option OTOOTDP When a Pumping System option is ordered along with the CIS Analyzer the entire analyzer consisting of the quadrupole mass spectrometer and its pumps is assembled tested and calibrated at the factory before being shipped The turbomolecular pump becomes an integral component of the CIS Head and the stored sensitivity factors are strictly valid when the CIS Analyzer is attached to a chamber Please consult SRS or you local representative for information on the available pumping options Users who already own a pumping station or who are putting together a custom or very specialized system might want to select their own pumps for the CIS Analyzer The following paragraphs are designed to aid those users in the selection of a pumping system that is best suited for the CIS Analyzer It is the user s responsibility to make sure that the pumping system ultimately chosen does not damage or limit the performance of the instrument For general information on vacuum system design and pump options consult 1 Gerhard Lewin An Elementary Introduction To Vacuum Technique published by the Education Committee of the American Vacuum Society 1987 2 J H More et al Building Scientific Apparatus Chapter 3 Addison Wesley Publishing Co Redwood City
76. to optimize the ion signals The plate with its small exit hole serves several purposes it separates the ionizer from the quadrupole assembly it draws the ions away from the ionization volume and it contains the ionizing electrons inside the source Electron leakage into the filter is only detectable at low mass settings 1 to 10 amu and can easily be eliminated biasing the extraction plate at negative potentials generally 40V is all that is necessary The electron emission current is the electron current from the filament to the ionization tube The available emission current range is 0 to 1 0 mA When an electron emission current is requested the CIS Analyzer biases the ionizer s electrodes and activates the filament s heater until the desired emission current is achieved A Background Filament Protection Mode is automatically enabled to monitor the performance of the filament while it is emitting electrons The Filament LED remains on as long as the filament is emitting electrons If a problem is detected in the operation of the filament i e burnt filament or overpressure the heater is immediately shut down and the problem is prompted by the LED s If a current of 0 mA is requested the filament s heater is shut down the repeller and focus plate are biased to ground the CDEM is turned off if necessary and the Filament LED is turned off to indicate the absence of emission in the ionizer The electron emission current is ve
77. to the ion current and sets the gain and bandwidth of the electrometer during measurements An increase in the biasing current results in lower I V gain and larger bandwidth but also means increased baseline noise due to the additional shot noise introduced by the extra current During regular mass scans the CIS Analyzer automatically adjusts the scanning rate and averaging to match the bandwidth of the detector The microprocessor calculates the total current flowing into the meter using the interpolation algorithm described above and subtracts the biasing current from the total to provide the actual ion current values used for averaging Obviously the amount of biasing current must be chosen keeping in mind the strong interplay between bandwidth i e acquisition rates and baseline noise i e minimum detectable partial pressures The single command NF Noise Floor supported by the RGA Windows program is used to program the electrometer s response Histogram scans analog scans and single mass measurements all share the same NF setting during measurements A decrease in the Noise Floor setting reduces the biasing current resulting in longer measurement times with cleaner baselines and lower detection limits As mentioned above the NF parameter value must be chosen keeping in mind the compromise between detection limit and acquisition speed When using the RGA Windows program to operate the instrument the Scan Speed CIS Quadrupole Gas Analy
78. using an optional electron multiplier CDEM measures an ion signal proportional to the ion current Use the Detection Control commands to choose the detector type FC or CDEM query the CDEM option recalibrate the electrometer s I V response and set the electrometer s averaging and bandwidth Use the CA command to zero the ion detector at any time Important Faraday Cup detection is the default setting when the CIS head is turned on Use the MO command to determine whether an electron multiplier option Option 01 is available in the CIS head being programmed The CDEM is available if the response is 1 lt LF gt lt CR gt The HV command activates deactivates the CDEM detector Its parameter value represents the bias voltage applied across the multiplier and determines the gain of the amplifier The null parameter HVO deactivates the CDEM and reconnects the FC detector to the electrometer Note The ElecMult LED reflects the status of the CDEM at all times A temperature compensated logarithmic picoammeter measures the ion currents collected by the FC or CDEM The microprocessor automatically configures the electrometer and connects its input to the correct signal based on the type of detector being used The sign of the electron multiplier currents is automatically reversed before the current value is sent out over RS232 so that the computer does not need to do any sign flipping on the currents received when the CDEM is activated The
79. value In mass to charge ratio units See also Peak width Resolving Power R M AMyoq Ratio between a particular mass to charge ratio M and the resolution AMyjoq at that mass Dimensionless ratio RGA Abbreviation for Residual Gas Analyzer RGA Cover Nipple CF Nipple that covers the RGA Probe Scan Speed mass spectrometer The speed at which the RGA scans through a range of succesive mass numbers Scanning The procedure of continuously changing the mass tuning of the quadrupole mass spectrometer to bring successive mass numbers into tune Sensitivity Partial Pressure The partial pressure sensitivity of the RGA to a gas g S g is defined as the ratio of the change H Hbo in principal mass peak height to the corresponding change P P in total pressure due to a change in partial pressure of the particular gas species Hg and Po are background values Sg H Ho P Po The units of S g are of ion current per unit pressure amp Torr for example Total Pressure SRS Quadrupole Gas Analyzers 6 Glossary of Terms The total pressure sensitivity of the RGA to a gas g is defined similarly as the ratio of the change H HA in total ion current to the corresponding change P P9 in total pressure due to a change in partial pressure of the particular gas species Ho and Po are background values Sensitivity calibration The act of establishing a a correspondence between the change in ion current and the corresp
80. 0 mbar without bypass pumping While it is possible to build a atmospheric sampling system based on a 1 4 meter 50 um glass capillary there are considerable reasons to use a bypass pump configuration Bypass pumping improves the operation of a system by increasing the flowrate of gas through the capillary about 3 4 orders of magnitude The higher flowrates and smaller pressure drop allow a wider selection of capillaries to be practical Stainless steel and PEEK capillaries are more affordable and flexible than glass capillaries A large flowrate means that the volumetric SRS Residual Gas Analyzer Appendix B 7 flowrate at the inlet of the capillary is more reasonable For a system with 70 liter s pumping speed operating at 10 mbar the volumetric flowrate at the inlet would be 70 nanoliter s Any dead volume at the inlet of the capillary would result in an unreasonable response time With such small flowrates inlet devices such as filters valves or connecting hardware cannot be used Overall the bypass pumped capillary system is more flexible and only requires a minor addition of hardware one valve and some tube The configuration seen in Figure 4 is made possible by the recent advances in hybrid turbomolecular drag pumps and diaphragm pumps Traditional designs would have relied on a two rotary vane pumps and standard turbomolecular pump The high compression ratios of the hybrid turbo pumps allow the two streams bypass and sample
81. 0 Remove the filament following the steps and precautions described in the Filament Replacement section of this chapter 11 Remove the short alignment rod located right in front of the anode slit 1 e between the two filament mount baseplates This rod will not be replaced Save it 12 Next remove the two filament mounts Two short alignment posts are separated from the baseplates during this step Save them in a safe place so they can be reattached during reassembly 13 The top alumina ring is now free to be removed from the ionizer exposing the anode s baseplate Remove the two screws that hold the anode s plate against the bottom alumina ring and pull out the tube assembly The short alignment rod will be removed during this step but it does not need to be replaced Save it 14 The bottom alumina ring is now free to be removed from the ionizer exposing the extraction plate Remove the single screw that holds the plate against the quadrupole s alumina spacer and pull out the plate CIS Quadrupole Gas Analyzer 15 16 17 18 19 20 2 22 23 lonizer Replacement 7 9 Use the new parts from the Ionizer Replacement Kit to replace the ionizer components Remove the old e clips from the loose alignment rods before they are reattached to the plates The new components are clean and vacuum compatible Avoid contamination Replace all components at once Discard the old ones Use a fresh screw f
82. 00 jumper is in the Calibration Disabled position Peak Tuning Parameters protected by the JP100 jumper 1 JP100 jumper is in the Calibration Enabled position Peak Tuning Parameters not protected by the JP100 jumper Parameters Only one possible command format is allowed CE Error Checking The only acceptable parameter is a question mark The absence of a parameter i e EC is treated as a bad parameter error Diparam param 0 255 Description DI Parameter adjust Peak Width Tuning command JP100 Jumper protected Echo Query Response Program the value of DI during the Peak Width Tuning Procedure The parameter one of four peak tuning parameters represents the DI value in bit units Warning Please read the Peak Tuning Section of the Tuning Chapter before using this command The CIS Head adjusts the DC levels of the quadrupole filter during measurements so that constant mass resolution is automatically available throughout the entire mass range of the spectrometer The bulk of the DC voltage is supplied by a DC power supply with an output linearly related to the RF amplitude The rest of the DC voltage DC Tweek is provided by the output of an 8 bit digital to analog converter DAC The firmware uses two Peak Tuning Parameters DI Intercept and DS Slope stored in the non volatile memory of the CIS Head to calculate the 8 bit settings of the DAC according to the linear equation DACH m DS m DI CI
83. 1 x 10 sec sec which is measured with a FC detector To measure smaller leaks a CEM detector can be used or the turbo pump can be throttled to decrease the pumping speed Supply Gas Valve Seats Leaks across valves that supply gasses to a vacuum system cannot be detected with conventional helium leak testers unless the valve supplies helium To test a suspect valve would require removing it and attaching it to the leak tester Because the RGA can monitor any gas this is unnecessary the valves on gas supply lines can be tested in situ The procedure is simple monitor the composition of the vacuum system with a high pressure and then a low pressure behind the valve seat in question If the partial pressure of the gas in question changes the valve seat is leaking Supply Gas Manifolds Leak testing supply gas lines can be a very trying experience The difficulty is mostly because compression type fittings do not have a leak test port Another difficulty is that supply manifolds commonly have a large number of connections in close proximity Because the leak in a compression fitting is inside the fitting transporting the test gas to SRS Residual Gas Analyzer Appendix A 13 the leak requires a large flowrate and waiting for an extended time for the gas to diffuse into the fitting Because of the flowrate and time it is possible that the test gas can travel to adjacent tube fittings and cause a misleading indication of a leak Often times
84. 2 75 CF flanges Use 1 8 turns in crisscross order 1 4 2 5 3 6 4 1 5 2 6 3 1 until the flanges are in contact and finish the tightening process with an extra 1 16 of a turn on each bolt Get an extra hand from a co worker if necessary CIS Mounting Flange Process Chamber Feedthru Flange CIS Cover Tee Vacuum Port Pumping System Port Figure 1 CIS Probe Installation Pumping System Installation The Pumping System usually attaches directly to the probe s Pumping System Port see Figure 1 Carefully follow the manufacturer s instructions while mounting and interconnecting the pumps and their controllers A typical upgrade to the Pumping System includes a total pressure gauge dedicated to monitor the pressure on the quadrupole rods If a total pressure gauge is part of the Pumping System install the gauge between the CIS probe and the pumps carefully following the manufacturer s instructions Additional vacuum hardware is usually required to accommodate the extra gauge As long as the pressure in the vacuum chamber is under 10 Torr start pumping down the CIS Analyzer as soon as all the vacuum connections are completed CIS Quadrupole Gas Analyzer 1 8 Installation If present use the Pumping System s total pressure gauge to check the pressure on the quadrupole rods Under normal operating conditions i e gas pressure 410 Torr in the process chamber and a well matched pumping system the pressure on t
85. 3 B3ZINU FHL XDJ 2 133HS 33S SIN3NDdWOUJ 3ZINOI 3H1 MOHS LON 300 ONIMVAO SIHL ATEWASSV 38U8d Z3 IDdrieovrit SIS JINSYIIIY ADJ NADMS aB33vdS vWIHTT Y D rf 2 ALIaVTD X03 ATBWISSY WO lavdv NADHS sas cr Gei HE ac 9f AB L6 274 U3IJIOOW 15v1 Mile NY SI 4 WHI I 1S310N AMJIA O3007dX3 OOE 002700i SIJ Sas m 030014X3 19 usn des NUUS 91219 1N30 3002 JDYNOS NOI 03S012 6r06 vr1 80r XVJ LvO6 PRL SOR NOIS30 Hd J unos NO 03S01 J HAMEN meen 21111 ONT AVEO HLIK SALLE INNJAY GOOMMV3Y 0 0621 ONT SWJLSAS HIYYISIY GYOINVLS 410 NOI 1d1 9S30 HINN LYYd 9 8910311015 GNNOY 08 0 20 1500 0 ue 08 0 000 S6100 0 3l z 881 0311015 0NNOa 7 000 96100 0 z HRC o D E EECHER O oo o 1 9 990 56180 0 mi EEN L W3HSVM Nie 000 81100 0 01 3ivid NOI12VHIX3 02L S8L00 L 11 QOY 1N3WNOI Tv 1N3Y1 j 0 L 61100 1 21 QOY 123NNO 1N3MY1 J O021 08100 1 1 INNON Nuf l3U IN3NY31 3 02L 8LL00 L v INNON AIAANSINIWYTII OZL LLLOO L SI Sd 1 HIM ININYIII 024 1100 L a URIS vNIWQv JNO 121 1 900 L Il 3ivig u31132338 02L 18L00 L 81 Appendix A Vacuum Diagnosis with SRS RGA s Introduction Residual Gas Analyzer RGA is the term for a class of mass spectrometers They are all quadrupole mass spectrometers and typically cover mass ranges from 1 to 100 or 200 amu atomic mass units
86. 4 8 Electro mel IM A 4 9 Detection limit vs scan rate llllieeeeieeeeseieieeeeseieeeeeiee nenne manns nhanh nn ntn nana nnmnnn EEEEE NEEN 4 9 Adjusting the Zero of the lon Detector eeeeeeeeeeeeeeeeeennnr nennen nnns 4 10 Mass Filter Power Supply e eeeeeeeieeeeeses esses eene nnen nnne nnn nnn n nina nasa sas n sse tn nasa sa ss sanas anneanne 4 11 Maintenance and Service ui ec nunne cesdace lace ei ege edd gt Desdacee tae Bei etic Ree Ad tetas 4 12 CIS Quadrupole Gas Analyzer 4 2 Introduction Introduction The SRS CIS Analyzer consists of a CIS probe and an Electronics Control Unit ECU which mounts directly on the probe s feedthru flange and contains all the electronics necessary to operate the instrument The basic setup is shown in Figure 1 CIS Mounting Flange CIS Cover Tee n To CIS lonizer N Pumping System Port Electronics Control Unit ECU d e CIS Quadrupole Probe Figure 1 SRS CIS Analyzer components The ECU is a densely packed box of electronics 3 x 4 x 9 that connects directly to the probe s feedthru flange and also to a host computer It includes several regulated power supplies a built in microprocessor control firmware and a standard RS232 communications port It is powered by either an external 24VDC 2
87. 5 lon Detector Positive ions that successfully pass through the quadrupole are focused towards the detector by an exit aperture held at ground potential The detector measures the ion currents directly Faraday Cup or using an optional electron multiplier detector measures an electron current proportional to the ion current Description The following figure describes the detector assembly including the electron multiplier option CDEM anode CDEM CDEM cone Exit Plate EL IIT TIE CDEN signal MEME meme I FC signal Faraday cup Probe flange Faraday cup shield Figure 7 Detector Components The Faraday Cup FC is a small stainless steel type 304 metal bucket located on axis at the end of the quadrupole It is shielded from the intense RF and DC fields of the quadrupole by the grounded exit plate which also provides some focusing of the ions into the detector A cylindrical tube FC Shield encloses the FC protecting it from the strong electrodynamic potentials of the adjacent rods and from collecting ions originated at sources other than the ionizer The signal is carried to the electrometer through a coaxial feedthru which extends into the ECU box and efficiently shields the small ion currents The FC is attached to the center feedthru with a push on connector and can easily be pulled out for cleaning or modification Notice that an electron suppressor electrode commonly found in several commercially
88. 5 19 Storing information in the CIS Head seesseeeeeeeeeeses seen ne enne nnne annt nnne nnana 5 21 Programming the Quadrupole Mass Filter eeeeeeeeeeeeeeeeeeeenee een nnne 5 22 Error Checking the CIS Analyzer esses eseeeeeeeeeeee nenne nnne nn nnn asina sn nna nn nnmnnn 5 23 CIS COMMANG Set 5 28 ltEUE idee El EE 5 29 bp HEP 5 29 UNI Ep 5 29 lonizer Control Commands a eeeeeeeeeeeeesseeene nennen nnne nn nna snnm nnn tn nhan nnns stans nnns nnns nsa 5 31 EEparam param 15 s105 Eden EE ee ae NEE ere 5 31 ELEparani param 0 00 5 3 50 5 2 ssa Ae see ise tre ir aee se tee o tese HORSE ea 5 31 IEparam param 0 1 EE 5 33 VEpatam param 0 7 150 5 ee eerte toe t e EES 5 34 Detection Control Commands 4 eeeeeeeeeee eene nn nasa manna aa daa a sa nsa AR AR RR 44 R4 RS As AR RR RR 44 ER KEEN 5 35 Contents vii GA 5 35 CI i o tee eee S DIO e et iere 5 36 HVparam param 0 2490 E T eae iletre Ete aeae EENE ENEE A E E Ra eia 5 37 MON oieee E Eege e dere 5 39 NEpa ram param O 5 3 ie ttp A E ENEE NOTENE EIN EE n EEEN 5 39 Scan and Measurement Commandis eres nunnur nennen nnne nn intr inns n nns tn nn nnes 5 41 D ug 5 41 Pisces eases ec
89. 5Amps power supply or an optional built in power module which plugs directly into an AC outlet Warning The ECU does not have any serviceable parts and does not require any routine maintenance All calibration procedures should be done using the RS232 interface and the CIS calibration command set During normal operation of the CIS Analyzer regulated power supplies built into the ECU set the electron emission current the voltage levels on the ionizer electrodes and the high voltage across the electron multiplier RF DC levels for each mass are also set and regulated by the ECU based on internal mass calibration parameters permanently stored in non volatile memory A built in logarithmic electrometer detects the ion currents collected by the FC or electron multiplier and converts them to voltage signals that are read by a built in A D converter The microprocessor automatically compares those signal voltages against an internal calibration and calculates the magnitude of the ion currents The ion currents are then averaged as needed offset corrected and transmitted to the host computer over RS232 for immediate display Several built in checks constantly monitor the operation of the probe and its operating environment For example the filament emission and the electron multiplier are immediately turned off in the case of accidental overpressure Active LED s on the rear panel of the ECU provide constant feedback on the status of th
90. 8 Notes e The new DI value must fall within the acceptable parameter range of the DI command e Achange in DI affects the width of all the peaks in the spectrum e A decrease in DI results in broader peaks at a rate of 0 036 amu per bit removed High Mass Peak Width Adjustment To modify the high mass peak width by an amount Am amus modify the value of DS from its original value DS to DS DS 28 Am m Notes e The new DS value must fall within the acceptable parameter range of the DS command e Modifying DS affects the width of peaks at the higher end of the spectrum An increase in DS results in the peaks getting sharper and a decrease in DS results in the peaks getting broader e The effect is more significant at the higher masses and that is why we do this adjustment second after the width has already been modified by the change in DI e If the mass to charge ratio of the low mass gas is real low this adjustment will have a small effect on the width of its peak Iterations In most cases it will be necessary to repeat the two width adjustments one or two more times until both low and high mass peaks show the desired widths Note Changes in the peak positions will also be observed at a rate of 0 40 amu per amu of increase in peak width and a Peak Position Tuning procedure will be needed to put the peak positions back where they belong Important The Peak Width Tuning Procedure can be used to adjust the resolu
91. Analyzer Partial Pressure Analysis Basics 2 17 adjusted to correct against the mass discrimination of the electron multiplier s gain Important Following current industry standards the partial pressure sensitivity factors stored at the factory correspond to Nz measured at 28 amu with Amjo 1 amu default ionizer settings for the corresponding mode of operation and Faraday Cup Detection Single gas measurement example Monitoring the concentrations of one or few components in a system is easy in the absence of severe spectral interference Suppose a system where argon is measured at 40 amu principal mass in the absence of any other gases that contribute a signal at that mass value The sensitivity to argon was previously measured at S 4 210 amps Torr RGA Mode and the electron multiplier is biased and its gain at mass 40 was previously measured at cpEM 1 0210 relative to the FC signal The partial pressure of argon DA is easily calculated measuring the intensity i e peak height of the ion current at mass 40 Io Par Lio gcpgM Sar units of Torr 4 The peak value Lio can be extracted from a spectral scan or measured directly using the single mass measurement mode of the CIS Analyzer For example a 10 amp peak value corresponds to 9 810 Torr of Ar Note that equation 4 is a particular case of equation 3 and that the fragmentation factor for the principal peak of Ar is one by definition CI
92. C detection mode Detector Programming Tips e Use the ElecMult LED to visually inspect the status of the CDEM during programming e Use the HV command to query the type of detector that is currently active The CDEM is active if a non zero voltage setting is returned to the computer e Check the value of STATUS returned after the HV command execution Bit 3 provides immediate information about the success of the command e The HV command checks for the presence of a CDEM option in the CIS Head before execution starts and an error is reported if no CDEM is available Please see EM command for details e tis possible to activate the CDEM if the filament is not emitting electrons but the CDEM will be deactivated by any overpressure that shuts down the filament e The correct operation of the electrometer can be tested using the Error Reporting command ED e The scan rates and signal to noise ratios for the different NF settings of the electrometer are listed in a table in the Electrometer section of the Electronics Control Unit chapter CIS Quadrupole Gas Analyzer Programming the CIS Head 5 15 e When using the RGA Windows program to operate the RGA the Scan Speed parameter setting available in the Scan Parameter Setups of the Scan menu is used to set the NF parameter value in the CIS Head according to the equation NF ScanSpeed 1 e Use the CA command to readjust the zero of the detector every time the detector
93. CA 1988 Pump Options Turbo pump based systems are by far the best choice for quadrupole mass spectrometers They are reasonably priced and provide the largest list of desirable features Small dimensions high pumping speed high compression ratio low base pressure minimal power and cooling requirements short start up time low noise low contamination from backstreaming oils low maintenance and operation in any orientation are some of their advantages when compared to other options Most turbo pumps operate at full pumping speed at inlet pressures above 1 mTorr Turbo pumps compatible with highly corrosive gases are also available Increased water pumping speeds can generally be achieved interposing a cryogenic water trap between the CIS analyzer and the turbo pump CIS Quadrupole Gas Analyzer 3 22 lon Detector Modern hybrid turbomolecular pumps offer increased compression ratios and can be backed by oil free diaphragm pumps providing ideal oil free operation This is the approach followed by SRS for its pumping systems and the one recommended by the factory for all CIS Analyzers A good quality oil trap must always be placed between a turbo pump and the foreline pump whenever an oil based mechanical pump is utilized Contamination from oils backstreaming through the vacuum pipes must be minimized at all cost in the CIS Analyzer Oil free pumping systems provide the best protection Diffusion pumps should not be used in comb
94. CES Ra Mounting Range RGA Cover Mipple hed pede hass Filter Wein Chamber g Pa 100 Toor dn geen Figure 1 SRS Open Ion Source OIS schematic 1 Repeller 2 Anode Grid 3 Filament 4 Focus plate The OIS penetrates into the process chamber The filament wire and the anode wire cage are open to the surrounding vacuum chamber All molecules that are moving around in the vacuum chamber can easily move through the ion source The pressure in the ionizer is the same as in the rest of the surrounding vacuum and also the same as in the quadrupole mass analyzer and ion detector The OIS is open to all the gaseous molecules in the vacuum chamber and can be used to monitor and detect changing gas levels as long as the overall pressure remains under 10 Torr Higher pressures result in a decrease in sensitivity due to space charge repulsion between ions Performance limitations of the OIS Overall most commercially available OIS RGA s do a very good job at measuring residual gas levels without affecting the gas composition of their vacuum environment However some potential limitations must be kept in mind particularly when the sensor is used routinely to monitor minute trace impurities i e PPM and sub PPM levels or UHV environments 10 Torr or less The following is a list of the different ways in which an OIS RGA can contribute to its background signals decreasing the detection capabilities of the sensor Ou
95. CIS Quadrupole Gas Analyzer 7 22 Quadrupole filter cleaning 10 Note the placement of all parts and their orientation before disassembly Begin by removing the filament following the necessary steps from the Filament Replacement procedure described in this chapter Next remove the CDEM following steps from the CDEM Replacement procedure Store the multiplier in a dry box or desiccator Loosen the seven set screws that fasten the 1 8 diameter rods to the feedthru connectors and remove the bowed e clip from the exit plate align rod that is located right above the CDEM You can now separate the entire quadrupole assembly from the detector feedthru assembly There are no serviceable parts in the flange Set it apart in a safe clean area Next separate the ionizer from the quadrupole filter by removing the e clips that hold the 1 8 diameter rods in place Store the ionizer electrodes in a safe clean area Disassemble the quadrupole and set apart the precision ground rods for cleaning This is a good time to carefully inspect all the components of the probe for damage and contamination Replace or clean any parts that are suspect Note We do not recommend cleaning the alumina spacers but if signs of severe contamination are evident ultrasound clean the two rings for 15 minutes with diluted cleaning solution and bake them out for 2 hours at 180 C after a thorough rinsing Rods cleaning Use the Micro Mesh abrasives to clean the rods
96. Com Utility is a simple Windows OS communication program that allows you to communicate with the CIS Head directly by typing valid CIS commands on your keyboard The program functions like any common terminal program where the typed characters are sent directly to the serial communications port and any received characters are displayed immediately on the screen The RS 232 communication parameters of RGA Com are fixed to be compatible with the CIS Head The only variable that may be selected is the communications port A list of up to nine COM ports is available to connect to the CIS Head RGA Com Fixed parameters e 28 8k Baud rate e 8 Data bits e No Parity e 2 Stop Bits Communicating with a Head To connect to an SRS CIS Head do the following Start the RGA Com program Select the Select Com Port command from the COM port Setup menu Select the Com port you want usually COM2 from the list box and press OK Select the Connect command from the COM port Setup menu Begin typing commands press Enter after each command to validate it Qv OE ume pe spen Es When you are done select the Disconnect command and exit the program CIS Quadrupole Gas Analyzer 5 4 The RGA COM Utility Tip e When you first connect to the head step 5 above send the ID command to verify the connection with the CIS Head This command will return the Model number Serial number and firmware version of the CIS Un
97. DACH m DS m DI where m is the mass in amu and DAC8 m is the 8 bit setting at that mass The purpose of the Peak Width Tuning Procedure is to determine the values of DI and DS so that all the peaks in an analog spectrum have the desired peak width typically 1 amu The DS command is used to program the value of the DS peak tuning parameter during the Peak Width Tuning Procedure The value is saved in the non volatile memory of the CIS Head and used by the firmware to generate DAC8 m during measurements Note to Supervisors A calibration disable jumper JP100 available on the circuit board can be used by a supervisor to block any attempt to modify the value of the DI parameter Supervisors may use this feature to prevent accidental changes in the calibration parameters by inexperienced operators Setting JP100 will disable peak tuning of the CIS Head Parameters DSparam param 0 8500 40 8500 If Calibration is enabled by the jumper JP100 See CE Command the value of DS in non volatile memory is updated and the internal scan parameters used to program the DC during scans and single mass measurements are updated accordingly CIS100 DS range 2 5500 42 5500 CIS200 DS range 1 2750 11 2750 DS Use this format to replace the peak tuning parameter with the original factory setting for DS The factory value is retrieved from memory and used as the new parameter value to excecute the command as above DS Query Returns the p
98. ET EE 4 4 Rear Pamel Rec C 4 5 Z4VDC 2 5A CONC OT oic id erc s iuo iude eraot NN du au sc ua EE ote buda cacao de a ec pa du aw RC a E a e Du a 4 5 RS232 DCE 28 8k Connector aae aaa a aae aa dest sdisscccescadecadicsaaueestaceesccacusentsaacecteeetes 4 6 LED S dE de eaea ea ae aas ated eas aaa ee dae aan edd eva tee deo ede eee ee eee 4 6 Locking Knobs niei decus ENEE NEEN ENEE EEN 4 6 Power entry module Option 02 eeeeseeseseeeeeiseeeeeeeeeenn nenne nnne nnn nn sana ennn nnmnnn nnn 4 6 LED F nctonallity eerte ere tee enne eet ere nere cnet tenere Letti een 4 7 STATUS Green LED See ae e pee dete eee ote pe dre eene ue 4 7 ERROR RedYLEED S cete re Ee eter re ee ERE T BEER RENE AUS 4 8 Electromelter inh er ee e ILLI I Lu uu ID II 4 9 CIS Quadrupole Gas Analyzer vi Contents Detection limit vs scan rate eeeeeeeeeeeeeeeeeeenee nennen nennen nennen nnmnnn nnmnnn nnmnnn inneren 4 9 Adjusting the Zero of the lon Detector esee nnne nnns 4 10 Mass Filter Power Supply 4 neeeeeeeeeses eiie eeenenee enne inns snnm nnn nn nn sinn nasa sant n ase sR assa sa sas mana sn Rusa na 4 11 Maintenance and Service 4 eeseeeeeiieeiieeseeseeeee ee eeen snas nhan nn nn inna sas ta sant n asa tR nass assa snas atn nnna 4 12 Chapter 5 Programming the CIS Head 5 1 Ittre eet ee EDEN 5 3 The RGA CO
99. Electronics Control Unit ECU CIS Quadrupole Probe Figure 1 SRS CIS Analyzer components The CIS Probe consists of a quadrupole mass spectrometer equipped with a high conductance differentially pumped CIS ionizer mounted inside a 2 75 Conflat Tee CIS Cover Tee It is described in detail in the Quadrupole Probe chapter of this manual The total probe equipment consists of three parts the CIS ionizer electron impact the quadrupole mass filter and the ion detector The closed design of the ion source allows the sensor to sample at total pressures as large as 10 Torr directly while at the same time attaining sub ppm detectability throughout the entire mass range In the absence of spectral overlaps i e overlapping background peaks the mass spectrometer sensor is capable of detecting gas impurity concentrations under the 100 ppb level The detector measures the ion currents directly Faraday Cup or using an optional electron multiplier detector Option 01 measures an ion signal proportional to the ion current The probe assembly is connected directly to the process chamber through its standard CIS Mounting Flange 2 75 CF connection The side port of the CIS Cover Tee i e Pumping System Port provides the connection for the pumping group required to differentially pump the CIS ionizer and keep the quadrupole mass analyzer and the filaments at high vacuum during process monitoring Please consult the Pumping System Requirements sect
100. FC signal output and reconfigured to measure positive currents e The firmware algorithms are reconfigured to transmit the magnitude of the positive currents measured e The HV LED is turned off e The STATUS Byte is sent out to prompt the end of the command HVparam param 10 2490 The parameter is the magnitude of the CDEM bias voltage requested the actual biasing voltage is negative The following steps are taken e The requested biasing voltage is applied to the CDEM e The electrometer is connected to the CDEM anode and reconfigured to measure negative currents e The firmware algorithms are reconfigured to transmit the magnitude of the negative currents measured e The HV LED is turned on e The STATUS Byte is sent out to prompt the end of the command HV The command is excecuted with the default parameter value Default 1400 Volts HV Returns the magnitude of the biasing voltage on the CDEM The number returned by the query command is the actual voltage available at the output of the HV driver and will always be very close but rarely identical to the one requested with the HVparam command Error Checking The CDEM option Option 01 must be available in the CIS head receiving the command or a bad command error is reported see MO command for details CIS Quadrupole Gas Analyzer 5 38 Detection Control Commands MO Number parameters must be within the accepted range and must be integers No parameter i e HV
101. L level e All output signals should be considered INVALID unless the Outputs Valid signal is set high when the RGA is scanning and acquired data has been validated e When the I O board is reset all the output signals are reset to Low TTL levels This happens anytime the computer is turned on or the I O board is initialized Introduction With the Output Control option the RGA Windows program controls TTL output signals that may be used in a variety of process control applications The 24 TTL signals 2 reserved for future use are located on a PC expansion bus that is installed in the same computer as the RGA program The user can access the TTL signals using a 37 pin cable and a universal screw terminal board An electromechanical relay board compatible with the TTL output connector and cable may be attached instead of the screw terminal to drive solenoids and other system components Signal Description Table Channel Outputs 11 output channels 10 TTL signals are mapped to the 10 channels associated with the Table P vs T and Annunciator modes The user assigns a trigger and hysteresis level for each channel independently When enabled the channel is monitored after each scan and when the pressure goes above or below the trigger value hysteresis the corresponding TTL bit is set high The user may temporarily override any channel by setting its output Low or High The Total Pressure value is the eleventh channel and is m
102. M B seme 5 3 INTOCUCUION m 5 8 Communicating with a Head a ssseeseeeeeesessieeee essen nente nnne pa snnm aoas aaae asa n anna 5 3 RS232 Iunio 5 5 LED INdiCators eege 5 5 Comma d Luc ere 5 6 Examples of command formatsioon telo me tete tiet eio et p eo ENEE 5 6 Programming tips 7 3 He HE e LIRE tette et ete LS 5 7 G mmu nicati n Errors isisi 5 8 Command CN 5 8 Parameter EEN 5 8 Jumper Protection Violation nesrin n E E E E E i E E E 5 8 Troubleshooting TOONS ugeet ee EE EE 5 10 Programming the CIS Head 2 1 Lcid dec dite e iter draden e eene deed edt Eege 5 11 Initializing the CIS Head ri eerte eer d Dv See eene 5 11 Programming the lonizer eeeeeeeeeee eene sene nnn nnne nn nnns nnmnnn nnmnnn nnmnnn nnmnnn nnna 5 12 Programming the Detector iiec dE eegend geed ege ger dH 5 13 Setting up Analog Scans eeeieeiieeeeeeeeeeee esee seen rrean reah daira nahana anni aapka Ekaan kan ant 5 15 Setting up Histogram Scans sssssesnseunneunrnunrnunnnunnnunnnunnnnnnnnnnnnnnnnnnnnnnnnnnn nunn nnnn anneanne nnmnnn nnna 5 17 Single Mass Measurements ccseccesceeseeeeeseeeeneeeeeeeesesnaeseseeeeneeeeseaesaseaeenseaeseeeseseaeseseeeeeenees
103. Mode Scan consists of a succession of individual single mass measurements over a pre specified mass range A single value is used to represent the peak heights at each integer mass within the range Histogram scanning is one of the most commonly used modes of operation for the CIS Analyzer Its two main advantages are a faster scan rate than analog scans and a reduced amount of data being exchanged and stored Histogram scans are triggered with the HS command The scan parameter can be set for single multiple and continuous scanning operation The mass range for the scan is set in advance with the commands MI Initial Mass and MF Final Mass A current value is transmitted for each integer mass value between MI and MF for a total of MF MI 1 measurements See HP command For maximum data throughput ion currents are represented as integers in units of 10 Amps and transmitted directly in hex format four byte integers 2 s complement format Least Significant Byte first The detector settings i e detector type and electrometer s noise floor setting to be used during the scans must be selected in advance with the NF and HV commands The zero of the ion detector is automatically readjusted at the beginning of each histogram scan so that the baseline is always centered around zero The offset correction factor calculated and stored in memory will then be automatically used to correct all currents measured under the same detector settings Th
104. NF settings NF The noise floor is set to its default value Default value 2 NF Returns the noise floor setting currently used by the electrometer Error checking Number parameters must be within the specified range and be integers The absence of a parameter i e NF is treated as an error CIS Quadrupole Gas Analyzer 5 40 Scan and Measurement Commands Scan and Measurement Commands AP HP Description Analog Scan Points Query Echo Query Response Query the total number of ion currents that will be measured and transmitted during an analog scan under the current scan conditions Important The query response does not include the extra current 4 bytes that is transmitted at the end of all analog scans Please see SC command for details The number of points 1 e ion currents retuned over RS232 is calculated based on the MI MF and SA parameter values Number of points MF MI SA 1 The first point corresponds to the mass MI and the other MF MI SA are from scanning to MF with SA measurements steps per amu Each point transmitted represents an ion current and as such corresponds to 4 bytes being received by the host computer The AP query is used to verify that the CIS Head and the host computer agree on the number of bytes that will be exchanged over RS232 during the analog scan The total number of bytes sent out to the host computer during an analog scan is obtained multiplying by four the
105. NI ceca uU aM DeL DI SEIL 7 17 nu 7 17 ele LC 7 17 Quadrupole filter cleaning 1eeeeeeeeeieeseeeee eese eeeeee seen nennen nnn nn anita snnm h nn tnn nsn tn assa sanis nnne nasa 7 20 mnm 7 20 Procedo sissic2cc3 ege E 7 21 SRS Probe Refurbishing Service eeeesieeeiieseieeeeses esee nennen nn nn anima natn nain nnns sita ss sna NENNEN 7 24 Contents ix Chapter 8 Troubleshooting 8 1 LED Ie 8 2 Internal Error Detection in the CIS Analyzer ssseeseeseeeeseeeees sienne nennen nnn anna nannte tnra nna 8 3 Basic Troubleshooting cisien eea raaa ENEE Eege 8 5 Built in Hardware Checks aieeaa iaaeaie aiene aoa aeaaee aiian aae daade ai haear aaa ade aada aa sa aad endende aantas aiai nnda 8 10 24V DC GT ET E 8 10 drpeuIjs E 8 10 Quadrupole Mass Filter RF P S eeeeeeeeseseeeeeieeeeeeeeeeee nnnm nnn nn nnn nn ania santa nnmnnn na 8 11 Filament s Background Protection mode eene 8 12 Chapter 9 Circuit Description 9 1 Overview ot He E D 9 3 Gireut Dessert DE 9 4 General Description 2 Ee 9 4 CIRCUIT Boards ieee c
106. NSE T2 essei eiieeeeees esee KEREN nasa sana nn tn nasi nasa sana nn n nnn nn 9 8 IA el nei re e Rede oer eret eode to e eee Tera ee een ene deve co tea ee aede o de eb o dress 9 8 AID COonverstOn Eet Pe eret Mee eel UN EE ede RN eere eM ge 9 8 Power up Conditioning uei Ue pee eerie reete ade edat ee Ee 9 9 Schematic name QMSE T3 geg Ee ege eege EE Ee ege Eed 9 9 DC Control Voltages a eet o t nd e tea toe estes 9 9 RE Ainphitude Detection repete tette de te ete dp ins 9 10 RE Amphltude Coritrol 4 nette EE EE 9 10 Foldback Current Ltn estener a eok reete Lio LR PES Ce e ER CERE CUR E ERR REEL ARRA 9 10 Schematic name ONSE B1 eeeeieeee ei iieeeeessene sena antena snas nnne asses asas s sena sa sano nasa nanne En 9 11 Mass filter RE Supply 54e ere em ete eet Hebe darse ecce eee pec ota 9 11 DC E EE 9 12 Schematic name ONSE BZ conie seruire Ce KEEN ENEE ENEE EEN 9 12 Filament Heater Supply netto tre tien eric tete oe gode esset tee oe Pega 9 12 Bias Regulatots 5 2 ep p erre eie teo a e teg esee Ie Mete dp elite eee 9 13 Schematic name QMSE B3 cieci sccees cade cnce esso SEENEN Ca aa Meo Dari OC Ca ead 9 14 Power Supplies utet Hed ere EE ee 9 14 Schematic name ONSE V1 ici REENEN sc cues dac ceca EES Eege Seed 9 14 Signal Conditioning EE beo e a IR De ee P a De eee pte 9 14 Schematic name QMSE V2 cda ges oet 3o ceed da aono Ue SE Yo Ir nnne nnm
107. Operating Manual and Programming Reference Models CIS100 CIS200 and CIS300 Closed lon Source Quadrupole Gas Analyzer SRS STANFORD RESEARCH SYSTEMS Revision 1 2 Oct 2011 Certification Stanford Research Systems certifies that this product met its published specifications at the time of shipment Warranty This Stanford Research Systems product is warranted against defects in materials and workmanship for a period of one 1 year from the date of shipment Service For warranty service or repair this product must be returned to a Stanford Research Systems authorized service facility Contact Stanford Research Systems or an authorized representative before returning this product for repair All users returning a CIS Analyzer back to the factory for repair and or service must submit a correctly completed Declaration of Contamination of Vacuum Equipment form along with the instrument The SRS personnel carrying out the repair and service of vacuum equipment must be informed of the condition of the components before any work is done on the parts A copy of the form is attached to the end of this manual Information in this document is subject to change without notice Copyright Stanford Research Systems Inc 1996 All rights reserved Stanford Research Systems Inc 1290 D Reamwood Avenue Sunnyvale California 94089 Printed in U S A Safety and Preparation For Use iii Safety and Preparation For Use WARNING
108. S Quadrupole Gas Analyzer 5 60 Tuning Commands where m is the mass in amu and DAC8 m is the 8 bit setting at that mass The purpose of the Peak Width Tuning Procedure is to determine the values of DI and DS so that all the peaks in an analog spectrum have the desired peak width typically 1 amu The DI command is used to program the value of the DI peak tuning parameter during the Peak Width Tuning Procedure The value is saved in the non volatile memory of the CIS Head and used by the firmware to generate DAC8 m during measurements Note to Supervisors A calibration disable jumper JP100 available on the circuit board can be used by a supervisor to block any attempt to modify the value of the DI parameter Supervisors may use this feature to prevent accidental changes in the calibration parameters by inexperienced operators Setting JP100 will disable peak tuning of the Head Parameters DIparam param 0 255 If Calibration is enabled by the jumper JP100 See CE Command the value of DI in non volatile memory is updated and the internal scan parameters used to program the DC during scans and single mass measurements are updated accordingly DI Use this format to replace the peak tuning parameter with the original factory setting for DI The factory value is retrieved from memory and used as the new parameter value to excecute the command as above DI Query Returns over RS232 the value of DI currently stored in memory E
109. S Quadrupole Gas Analyzer 7 18 CDEN Replacement 5 Turn off the pumping system and pressurize the quadrupole chamber to atmospheric pressure levels 6 Without disconnecting the CIS Cover Tee from the vacuum port remove the six bolts from the feedthru flange at the end of the probe and slide the entire quadrupole assembly out of the vacuum tube Note the rotational orientation of the Feedthru Flange before removing the probe assembly from the vacuum system so that the probe can be reattached in the exact same way it was at the end of the procedure Mark the side of the flanges with a permanent marker if necessary The ionizer the filter and the detector are now fully exposed and easily accessible The alumina seal SRS 7 00787 remains attached to the CIS Port held in place by a c clip CIS Mounting Flange Feedthru Flange Process Chamber CIS Cover Tee lonizer Vacuum p Probe Assembly EES d Pumping System 2227775557 Figure 3 Probe Removal for CDEM Replacement 7 Carry the probe to a clean dust free area immediately Avoid contamination using handling procedures compatible with high vacuum clean room requirements 8 Hold the probe in a secure upright position and do a thorough visual inspection of the unit Check for loose damaged misaligned and severely contaminated components Carefully inspect the ionizer and if any problems are detec
110. S Quadrupole Gas Analyzer Chapter 3 Quadrupole Probe This chapter describes the design and principles of operation of the components of the CIS Analyzer Probe In This Chapter Intro EH 3 2 jig E NE 3 3 Description i229 cence eee tee eis chui DUI das ea eee eM cee stareess 3 3 Principle of op ration EENE EEA NE AENA AAEE EAEE 3 4 Parameter Settings ege aeara a aaee aaiae aiae aaae aa adea aaa aeh Dee 3 6 Quadrupole EECH UE 3 9 rri EE CR EET 3 9 Principle of operation 1 cc eeLe ccce cie crec reis correre ee nL resi ime eua siad eaa nnmnnn d noB cma ENEE 3 10 Mass Range Resolution and Throughput eese 3 12 Zero Blast Suppression a eeeeeeieeeeeeeiieee seine nete nein nn annnm n annm na nn tnn santa ennnen ennnen nnns 3 14 aNPIlanIM Im rnc 3 15 Description bec 3 15 Faraday Cup Operation 1 4 ect Lice tiec rese erre Lace EENS EEEEEVE SEENEN EENS 3 16 Electron Multiplier Operation neeeeeeeeeees sienne nennen nennen nennen nennt nina nnn nnn tn nana ns 3 16 Upgrading to an Electron Multiplier Detector eere 3 19 Pumping System Requirements eeseeseeieeseieeeeeeee seen enn nn nnne nn ansia sana natn nasa nasa sana nnns sana nna 3 21 Pump ODpLUOLIS eere tenue eeu Eech 3 21 CIS Quadrupole Gas Analyzer 3 2 Introduction Introduction The Closed Ion So
111. S to obtain information on this very fast and convenient service Important All users returning a CIS Probe back to the factory for repair and or service must submit a correctly completed Declaration of Contamination of Vacuum Equipment form along with the instrument The SRS personnel carrying out the repair and service of vacuum equipment must be informed of the condition of the components before any work is done on the parts A copy of the form is attached at the end of this manual CIS Quadrupole Gas Analyzer Chapter 8 Troubleshooting This chapter describes basic troubleshooting procedures for the CIS Analyzer In This Chapter MarnihgS x Ennii enun cehacetesSacagcs Anis cuhcuduxsbhnso usc 8 2 Internal Error Detection in the CIS Analyzer ssseeesseeeeeeeeeeees esee nennen nennt nannten intensa 8 3 L1 MET dp 8 5 Built in Hardware Check cade cscsccsceceecetechscghececckcatecsectessaneezencedsatsegseczcodcedeatardsanessusedseatezse 8 10 24V DC Power app 8 10 diei area iaa NAN EANET EEEa EE EAEE 8 10 Quadrupole Mass Filter RF P S sssssnnssnnenunennnnnunnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nnn as 8 11 Filament s Background Protection mode esee eene nennen 8 12 CIS Quadrupole Gas Analyzer 8 2 Warning
112. V The 70 eV setting i e CIS 70 mode provides spectra that are virtually identical to those obtained from RGA detectors The 35 eV setting i e CIS 35 is commonly used in sputtering monitors to eliminate the Ar peak 350 ppm for 70 eV electrons that interferes with water detection at 18 amu Typical sensitivities are in the order of 10 Amp Torr for 70 eV electrons and very linear sensitivity response is observed all the way up to 1 mTorr of total pressure The overall sensitivity of the CIS Analyzer in the CIS Mode is about two orders of magnitude lower than what is observed in a typical RGA however the larger density of molecules in the ionizer makes up the difference and results CIS Quadrupole Gas Analyzer 2 10 Basic Operating Modes in ion currents very comparable to those observed in conventional RGAs A slight decrease in sensitivity is often observed when the electron ionization energy is reduced from 70 eV to 35 eV MDPP levels as measured with the FC are in the order of 10 Torr and can be easily improved up to three orders of magnitude using the CDEM s gain The MDPP values clearly indicate that the CDEM must be activated in order to obtain sub ppm detectability CIS Quadrupole Gas Analyzer High Pressure Sampling P gt 1 mTorr 2 11 High Pressure Sampling P gt 1 mTorr A Pressure Reducing Gas Inlet System PRGIS must be used in combination with the CIS Analyzer to sample gas pressures above 2 10 Torr In its most
113. _1 Middle bit of 16 bit A D converter s input multiplexer Q5 MPX_2 MSB of 16 bit A D converter s input multiplexer Q6 EMIT_CTL Filament heater duty cycle control O direct 1 regulate Q7 GRID_SEL Low for low grid potential high for high grid potential The MISC port QO RF ON Low to turn off RF high to turn on Ql IONS_OFF Pulse high for 50 ms to reset relay and ground FC Q2 IONS_ON Pulse high to set latching relay so FC signal enters I V Q3 MULT OFF Pulse high to ground e multiplier anode Q4 MULT_ON Pulse high to connect e multiplier to I V Q5 LINEAR Pulse high for linear I V converter offset calibration Q6 R C Set high to read 16 bit A D low to initiate conversion Q6 CS_VETO Set high to prevent or release CS to 16 bit A D converter Clocks The master clock of the system is an 11 0592 MHz crystal oscillator This frequency was selected for the following reasons 1 2 It is close to the maximum operating frequency for the 68HC11 12 MHz When divided by four it provides a usable RF frequency 2 7648 MHz When divided by 128 it provides a clock for switching power supplies 86 4 kHz When divided by 256 it provides a clock for the high voltage DC DC converter When divided by 384 it provides an exact PC baud rate 28 8 kbaud When divided by 2 it provides a A D convert rate 675 Hz CIS Quadrupole Gas Analyzer 9 8 Description of Schematics Since the A D convert rate is a sub multiple of all the ot
114. a PCM series card b Select No when asked if you want to install Universal Library or LabView software c Select YES when asked if you want the AUTOEXEC BAT file modified 5 Reboot the computer 6 Run the Instacal exe program from the I O board directory that you specified in the Install exe program above 7 Configure the Instacal program for your board name and settings see the Computer Boards INC manual for your board Make sure you run the internal test routines to verify that the board is functioning correctly 8 Start the RGA program and select the Setup Output Card command from the Output Control menu 9 Press the Scan for I O Boards button If you get a warning message select Yes to proceed with the scan At this time the board name and number should appear in the dialog box If the board is not found by RGA run the Instacal program and test the board to make sure it is operating correctly RGA Software Operation Please refer to the On Line Help documentation of the RGA program for a full description of the software SRS Residual Gas Analyzer Appendix D PPM Level Gas Analysis The Closed lon Source CIS Advantage Introduction Quadrupole Mass Spectrometers are used in a large variety of analytical applications from basic research to on line process monitoring and control Ease of use a compact design excellent dynamic range and very stable operation are some of the main features that
115. a low pressure and the quality of the vacuum is checked for leaks and harmful contaminants CIS Quadrupole Gas Analyzer Basic Operating Modes 2 9 The electron ionization energy is 70 eV so that the mass spectra show fragmentation patterns identical to those obtained with conventional Residual Gas Analyzers RGA The electron emission current is set to 0 5 mA to bring the sensitivity to levels comparable to those expected from conventional RGA s Under these operating conditions typical sensitivities are in the order of 10 Amp Torr or better This sensitivity is about an order of magnitude lower than what is observed in a typical RGA however the difference can easily be made up by running the electron multiplier at higher gain levels The sensitivity remains constant from UHV until pressures as high as 10 Torr The MDPP levels as measured with the Faraday Cup FC detector are in the order of 10 Torr and can be improved by three orders of magnitude using the CDEM s gain CIS Mode 10 lt P lt 10 Torr In the CIS mode the ionizer is exposed to pressure levels between 10 and 10 Torr and used for on line process monitoring and quality control This mode is used for example during the second stage of a sputtering process after the chamber is backfilled with a few mTorr of Ar and sputtering is started By far the most common application of the instrument in the CIS Mode of operation is to monitor process gas purity at the poi
116. a retaining ring Make sure the crescent washer SRS Part 0 778 is still attached to the anode tube Otherwise use long pliers or a long wire to remove the washer from the inside of the CIS Cover Tee CIS Mounting Flange Feedthru Flange Process Chamber lonizer Vacuum Bau Probe Assembly fu Pumping System 2227075555 Figure 2 Probe Removal for Filament Replacement 7 Immediately carry the probe to a clean dust free area and secure it in an upright position Avoid contamination using handling procedures compatible with high vacuum requirements 8 Using the clean flat head screwdriver to disconnect the repeller plate from its filament post fully exposing the filament and the anode slit 9 Before touching the filament visually inspect the entire ionizer Check for loose damaged misaligned and contaminated components Some discoloration centered around the anode slit is normal If problems are detected a complete Ionizer Replacement procedure should be carried out at this time Otherwise continue with the filament replacement procedure as follows 10 Inspect the filament and become acquainted with the way in which it is mounted on the filament posts Regardless of its composition the filament consists of a straight wire with a stainless steel square washer i e mounting tab spot welded to each end Precision machined slots define the exact
117. actors previously stored in memory are cleared after a complete calibration of the electrometer is performed see CA command for more information CIS Quadrupole Gas Analyzer 5 36 Detection Control Commands Parameters Only one possible command format is allowed CL Error Checking An attempt to pass any parameter with CL results in a bad parameter error being reported HVparam param 0 2490 Description Electron Multiplier High Voltage Bias setting Echo STATUS error byte or Query Response Set a negative high voltage across the electron multiplier CDEM connect the CDEM signal output to the electrometer and reconfigure the electrometer and current measurement algorithms to handle negative electron currents The parameter value represents the magnitude of the bias voltage in units of Volts Warning This command only works in heads with the CDEM option Opt01 installed See MO command Since the CDEM turns ion signals into amplified electron currents the CIS Head automatically reconfigures the electrometer to measure negative currents when a finite biasing voltage is selected The current measurement algorithm is also automatically reconfigured so that the magnitude of the currents measured is transmitted over RS232 The host computer can then handle the amplified signals the same way it did with the positive ion currents i e it does not need to flip the sign of the currents received The HV LED reflec
118. ailable in instruments with the CDEM option Option 01 installed See MO command for details and usually store a calibrated pair of gain high voltage values for the CDEM Programming example The following list shows a typical application of the storage commands to save head specific information in the CIS Head The first two lines store a partial pressure sensitivity factor of 10 0microA Torr into the first location of the storage table i e typically the RGA Mode Sensitivity for N2 The next two lines store a partial pressure sensitivity factor of 1 0microA Torr into the second location of the storage table i e typically the CIS 70 Mode Sensitivity for N2 The following two lines store a partial pressure sensitivity factor of 0 5microA Torr into the third location of the storage table i e typically the CIS 35 Mode Sensitivity for N2 The last two lines store a 1400V 10 000 gain calibrated pair for the CDEM XAI Select the first location of the parameter table XV10 0 Store the measured RGA Mode sensitivity in microA Torr XA2 Select the second location of the parameter table XV1 0 Store the measured CIS 70 Mode sensitivity in microA Torr XA3 Select the third location of the parameter table XVO0 5 Store the calculated CIS 35 Mode sensitivity in microA Torr MV 1400 CDEM HV setting for MG gain 1400 V MG10 CDEM gain 9 MV setting 10 000x Programming the Quadrupole Mass Filter The ML Mass Lock command activates the quad
119. al Operation Chapter of this manual Parameter Settings The parameters that affect the ionization efficiency of the CIS are electron energy ion energy electron emission current and extraction voltage The general principles by which they affect the performance of the source are well understood The ECU contains all the necessary high voltage and current supplies needed to bias the ionizer s electrodes and establish an electron emission current The ionizer settings can be directly controlled and monitored by the user through the instrument s high level command set or from simple menu selections within the RGA Windows software The following table summarizes the ionizer settings available to the user for the two basic modes of operation of the CIS Analyzer For details on the two modes of operation consult the Basic Operating Modes section in the General Operation chapter of this manual CIS Parameter Units Programmable Minimum RGA CIS range Increment Mode Mode Ion Energy 4or8 Electron energy 15 to 105 70 or 35 Extraction Voltage V 0 to 150 40 def 40 def Emission current mA 0 to 1 0 5 0 05 The average electron energy expressed in eV is equal to the voltage difference between the filament and the anode tube and can be set anywhere in the range of 15 to 105 eV For electrons to produce ionization of gas molecules by bombardment they must have a certain minimum kinetic energy This minimum energy is called the ionization pot
120. an is triggered Setting up an analog scan The following list of commands sets a scanning range of 10 to 150 amu the fastest scan rate minimum averaging 0 1 amu steps and after checking the number of currents to be measured per scan not including extra value sent at the end it triggers 10 analog scans Each one of the 10 scans transmits 1401 ion current values plus one extra current that is not displayed Each current is 4 bytes long MI10 Initial mass 10 amu MF150 Final mass 150 amu NF7 Fastest scan rate selected SA10 Steps amu 10 AP Analog Points query The number 1401 is echoed Add one for extra current SC10 Analog Scan trigger 10 scans are generated and transmitted Analog Scan Programming Tips It is good programming practice to follow each command that sets a parameter with a query of the parameter setting For example the first command in the list should be followed by a MI and a number 10 should be echoed by the CIS Head Notice that MI and MF are shared by analog and histogram scans Any command sent to the spectrometer during scanning will immediately halt the scanning action and clear the instrument s transmit buffer Remember to also clear the computer s receive buffer to reset the communications The command responsible for stopping the scan will be executed The CIS Head has the ability to store a complete scan in its output buffer The scan remains in memory until all the data is transmitt
121. and 1 to 300 amu CIS300 The main difference between the three models is given by the maximum supply voltage available to the rods The terms Resolution and Resolving Power are often used by mass spectroscopists to express the ability of a mass filter to resolve ions having different masses Resolution or Absolute Resolution AM oz The width AM of the pass band of the filter defined as the full width at which the 1on current falls down to 1096 of the maximum value Units amu Resolving Power R M AMio Ratio between a particular mass M and the resolution AMjo at that mass Dimensionless ratio It is common practice in modern quadrupole based partial pressure analyzers to keep AM ios constant at a value which insures adequate separation of masses that are 1 amu apart The quadrupole in the SRS CIS Analyzer operates in that Constant Resolution or Constant Am mode AM is preset at the factory to 1 amu but it can easily be adjusted by the user all the way to the theoretical ultimate resolution of the filter The following figure illustrates the resolution concepts explained above using a Krypton mass spectrum as an example The different isotopes of the gas are well separated from each other and a 1 amu peak width Amjox is measured on the kr peak at 10 of its peak height Also notice the 20 valley between the Kr and Kr peaks CIS Quadrupole Gas Analyzer Quadrupole mass filter 3 13 Torr 45E 08
122. and excecution is over Parameters This command is a query and can only have one parameter format ED CIS Quadrupole Gas Analyzer 5 56 Error Reporting Commands EF EM Error checking The only acceptable parameter is a question mark The absence of a parameter i e ED is treated as a bad parameter error Description FIL ERR Byte Query Echo FIL ERR Byte Query the value of FIL ERR The FIL ERR byte value is returned to the computer in ASCII format and with a lt LF gt terminator FIL ERR can only be modified by the Filament Protection Mode which constantly monitors the filament while it is emitting electrons No errors are present as long as the byte value is zero A non zero FIL ERR byte is only cleared after the filament s heater succesfully i e no detected errors establishes a finite electron emission current Consult the Error Byte Definitions section of this chapter for detatils on the different error bytes of the CIS Analyzer Consult the Troubleshooting chapter of this manual for possible causes and solutions to any problems reported Parameters This command is a query and can only have one parameter format EF Error checking The only acceptable parameter is a question mark The absence of a parameter i e EF is treated as a bad parameter error Description CEM ERR byte Query Echo CEM ERR Byte Query the value of CEM ERR If no electron multiplier CDEM is available the abs
123. and extending filament lifetime The filament is easily replaced by the end user in a few minutes without any need to take apart the ionizer Consult the Filament Replacement section of the Maintenance Chapter in this manual for a complete filament replacement procedure The tight design of the filament electron slit region makes it very easy for the filament to maintain the requested emission currents even under the lowest accelerating fields As a result the CIS is very comfortable operating with 35 eV electrons In factory tests and in the absence of reactive or corrosive gases tungsten filaments were operated continuously for weeks at a time without any degradation in performance or burn outs Principle of operation The filament is the source of the electrons used to ionize the gas molecules It operates at a negative potential relative to ground and is resistively heated to incandescence with an electrical current from the emission regulator The thermionically emitted electrons are accelerated towards the emission slit of the anode which is positively charged with reference to the filament and ground Most electrons do not strike the anode wall but rather pass through the emission slit and into the ionization volume where they create ions at the process pressure through electron impact ionization Electrons which pass CIS Quadrupole Gas Analyzer lonizer 3 5 through the ionization volume without colliding with any molecules are simply
124. arameter value currently saved in memory over RS232 Error checking The absence of a parameter i e DS is treated as an error in the parameter This parameter is protected by an internal jumper JP100 and a Protection Violation error will result if the jumper is in the Calibration Disabled mode See CE command Riparam param 86 0000 86 0000 none Description RF Driver output 0 amu Peak Position Tuning command JP100 Jumper protected CIS Quadrupole Gas Analyzer 5 62 Tuning Commands Echo Query Response Warning Please read the Peak Tuning Section of the Tuning Chapter before using this command Program the output of the RF Driver 0 amu during a Peak Posion Tuning Procedure The parameter one of four peak tuning parameters represents the voltage output selected for the RF Driver 0 amu in mV The magnitude of the RF determines the mass to charge ratio of the ions that can pass through a quadrupole mass filter without striking the rods i e with stable oscillations A linear relationship between mass and RF amplitude is one of the most attractive features of these type of filters The regulated output of the RF source that powers the quadrupole rods is controlled by and linearly related to the voltage output of an RF Driver circuit A linear relation exists between the output of the RF Driver the RF amplitude on the rods and the mass setting of the filter The purpose of a Peak Position Tuning
125. are no electronics components inside the CIS Probe This information is provided for the exclusive use by qualified technical personnel during service and repairs Warnings e The ECU is to be serviced by qualified technical personnel only There are no user serviceable parts inside Dangerous voltages capable of causing injury or death are present in this instrument Use extreme caution whenever the ECU covers are removed Do not remove the covers while the unit is plugged in Always disconnect the power before removing the covers of the ECU In This Chapter Overview usur dice EEN 9 3 iii tha cessas 9 4 General oceans 9 4 CIRCUIT BOARS me 9 5 Description of Schematics a eieeeeieeeiie esses a Ea ae aa aaa ra natn nhi e nasa natn nnns snas sanas masa anian 9 6 Schematic name QMSE T1 iiie ces nnnm een de ecu eva nn curva ar xeu vo Sp exa exa oe Pra v va SE ER XB dp evus 9 6 MiCrOprOGCeSSOE ce cte eee t a eese ect o t bee eee eee 9 6 Digital VO Potts 2 neta tte eder pe Ee eee e eee aed i Rt eee ene etd 9 6 The LED pott IR ettet ti ette eee eite Dee e oe ETE ee Eod Ue ecto doc idee 9 7 The MPX port EE 9 7 Th MISC EE 9 7 CLOCKS 7o et eee eme tel eec ee Pate Fee ree aes os al 9 7 RS232 IntetiaCcexicaucac e duni ed i idan ed ex ERE EE SE EE 9 8 CIS Quadrupole Gas Analyzer 9 2 Schematic name O
126. are used to read error bytes and to confirm internal parameter values The question mark must be strictly followed by a CR terminator With a few exceptions the data returned by most query commands is a string of ASCII characters terminated by a linefeed lt LF gt decimal ASCII value 10 and a CR terminator string lt LF gt lt CR gt No parameter Some commands do not require a parameter The CIS Analyzer assumes a potential command string has been received over RS232 when a CR character is detected in the serial interface A command handler immediately analyzes the string and if everything checks the command is executed However if a problem is encountered a communication error is reported and no command execution takes place The CIS Analyzer has a 140 character input buffer and processes commands in the order received If the buffer fills up the instrument s processor holds off handshaking on the RS232 interface using the CTS line Similarly the CIS Head has a 32 000 character output buffer to store outputs until the host computer is ready to receive If either buffer overflows the entire buffer is cleared and the error is reported Linefeed characters lt LF gt decimal ASCII value 10 and single carriage returns lt CR gt decimal ASCII value 13 transmitted from the host computer are ignored by the serial interface Examples of command formats The following list of commands activates the ionizer and triggers a s
127. as in order to assure accurate readings over its 8 decade range A programmable voltage source U209 and associated components can provide voltages from microvolts to volts which are applied to the I V converter via a 1GQ resistor to generate calibration currents from femtoamps to nanoamps The calibration source is also used to bias the I V converter during scans to establish the bandwidth noise floor tradeoff A second I V converter channel is biased by the calibration source to allow for temperature compensation of the detection channel Both I V converters are biased by equal currents from the calibration source so that their output voltages are nearly the same when there is no ion current being detected The outputs of each I V converter may be read via the 16 bit A D for calibration and offset nulling The outputs of the I V converters are subtracted in a differential amplifier U211A with a gain of 5 23 and a bandwidth of 1 kHz The differential amplifier is followed by a Butterworth filter U211B with a gain of 1 59 a 3 dB point of 300 Hz and a roll off of 12 dB octave The filter is used to reduce the noise on the signal which is above the Nyquist bandwidth for a 675 Hz sampling rate In low bias current cases the bandwidth of the signal is much lower per the diode time constant R233 insures that the output of the filter cannot exceed the 5V range of the 1 8 multiplexer at the input to the 16 bit A D converter A D Conversio
128. ased sputtering system you must solve two problems 1 Background contribution of water outgassing from the sensor 2 Interference at m e 18 from TA A thorough bakeout can reduces the background water contribution to the low tens of PPM levels but eliminating the Ar interference requires the use of several tricks that are used by most RGA users As usual some of those tricks work better than others Some users simply choose to monitor the m e 17 peak due to the OH water fragment For 70 eV ionizing electrons this peak is four times smaller than the main one at 18 amu This results in a significant reduction in sensitivity for water detection and also adds the problem of abundance sensitivity while trying to measure the mass 17 intensity next to a large AT peak at 18 amu A better option and the one recommended for RGA s with programmable ionizer voltages is to operate the ionizer with the electron impact energy reduced to lt 40eV This ionization energy is below the appearance potential 43 5eV of Ar For example the peaks at masses 18 19 and 20 due to Ar disappear while operating an RGA with 35 eV electrons and this is achieved with minimal reduction in the sensitivity of detection of Ar at 36 38 and 40 amu Reduction of the electron energy usually imposes an extra load of work on the filament and will reduce its lifetime However the reduced interference effects offset the extra costs of filament replacement As we wil
129. ated with the CL command e The zero of the ion detector is also automatically readjusted at the beginning of each analog and histogram scan so that the baseline is always centered around zero In order to correct the mass axis against peak position shifts caused by small temperature fluctuations the CIS Analyzer characterizes the voltage output of the RF driver s control circuit and recalculates its internal scan parameters to assure that the correct RF levels i e as specified by the last Peak Tuning procedure are programmed on the QMF rods as a funtion of mass Important Use a complete Peak Tuning Procedure to correct the mass axis calibration when large temperature fluctuations are suspected The calibration procedure triggered by the CA command cannot correct the mass axis against large temperature drifts that affect the response of the RF Driver to its controlling voltage or the relationship between mass and RF levels in the QMF itself 1 e due to changes in the QMF s physical dimensions CIS Quadrupole Gas Analyzer CL Detection Control Commands 5 35 Notes e The mass axis correction procedure can also be triggered at any time using the RS and RI commands with no parameters See Tuning commands e The mass axis correction procedure is also automatically performed at the beginning of all analog and histogram scans However no correction is performed at the beginning of single mass measurements since the extra checking
130. ave a self inductance of about 16 uH so as to resonate at 2 7648 MHz with the capacitive load presented by the rods in the mass filter together with the parasitic capacitance of the secondaries The primary of the transformer is a single turn driven by a square wave voltage at 2 7648MHz through a series inductor T401 of 0 54H The step up transformer is driven slightly off resonance so that its input has a capacitive reactance which resonates with the 0 5uH inductor at the drive frequency This approach is used to reduce power losses in the drive circuit the FETs are switched when the current is nearly zero and to reduce the distortion in the RF output as the drive current is very nearly sinusoidal Due to variations in the core material used in the step up transformer each unit must be tuned by adding capacitors across the primary This is done by programming the unit to operate at 100 amu and by finding the combination of capacitors connected between J401 and J403 which minimize the drive voltage as measured at J400 which is RF CT 5 Polypropylene capacitors with a voltage rating of 50V are used to tune the primary reactance for minimum power loss The 39 turn secondaries are wound in a very special fashion the two windings are placed side by side so that the magnetic flux seen by the two windings is very nearly identical Measurements on these transformers show a difference in self inductance between the two secondaries of less than
131. be cleaned immediately See CDEM Refreshment procedure in this chapter Storage CDEM s can be stored indefinitely in a clean dry container such as an air or dry nitrogen filled dry box Double bagging with clean dust free zip locked bags also works well as a temporary alternative CIS Quadrupole Gas Analyzer CDEM Pre conditioning 7 15 CDEM Pre conditioning Use the following steps on the first pump down and initial operation of a new CDEM 1 Pump overnight prior to initial application of voltage 2 Begin operation at the lowest voltage possible working up to the voltage required to produce observable peaks 3 Limit the initial operation to trace peaks with gradual increase in abundance levels over the first two hours of operation of a new CDEM All CDEM s undergo an initial cleanup phase during which absorbed gases are removed from the active surface If during this time the detector is exposed to high input currents permanent gain degradation by as much as a factor of ten may result The steps described above help to control initial outgassing and are performed in order to precondition the CDEM Optimum sensitivity and longer lifetime will result if the recommendations are followed CIS Quadrupole Gas Analyzer 7 16 CDEN Refreshment CDEM Refreshment A CDEM contaminated with organic impurities i e pump oil can sometimes be refreshed following the cleaning procedure described in this section The CDEM should show a
132. be is highly recommended before operating the CIS Analyzer again Retune the sensitivity of the CIS Analyzer following the instructions in the Tuning chapter before using the unit for any quantitative measurements CIS Quadrupole Gas Analyzer 7 10 Filament Replacement Filament Replacement The filament eventually wears out and needs to be replaced There is no need to send the CIS Probe back to the factory for this service The replacement procedure is simple and can be completed in a few minutes by qualified personnel Two kinds of filament materials are available for the CIS Ionizer W standard O100RFW Replacement Kit and ThO Ir optional OTOORFT Replacement Kit Make sure the correct filament spares are available before the replacement procedure is started The filament is very delicate and should be handled with extreme care The thoria coating in ThO Ir filaments is very delicate and can easily be damaged if the filament is mishandled W wire becomes brittle over time and often breaks when it is handled Please read the following handling recommendations before opening the filament s box Handling and care of the filament Do not bend or twist the filament Do not scratch the coating in ThO Ir filaments Do not handle the filament directly with your fingers use fine tweezers and hold it by the square tabs only Do not attempt to clean the filament Use only SRS supplied filaments as replacement Equipment Pro
133. bed next Work on one spacer at a time using a single small turn of the screwdriver on each screw After a single round of eight screws hold a spacer in each hand and slightly torque the assembly back and forth about its axis to make sure the rods are comfortably seated on their alignment grooves Repeat this tightening procedure one spacer at a time constantly checking the alignment until the spring washers are completely compressed Once the CIS Quadrupole Gas Analyzer 11 12 13 Quadrupole filter cleaning 7 23 quadrupole assembly is completed mount the CIS ionizer on it but do not install the filament at this time Use new e clips to hold the ionizer plates against the top alumina spacer but do not install any e clips on the bottom grooves of the connection rods at this time Next mount the quadrupole assembly on the exit plate of the feedthru flange and secure it in place tightening the connector set screws and inserting the necessary e clips Insert the rest of the rods in their correct locations and while checking for the correct alignment of their grooves and slots tighten the rest of the feedthru connector set screws Once the rods are in place attach the two RF ribbon connectors to complete the quadrupole filter assembly If the CIS probe has a CDEM mount the multiplier at this time Adjust the HV connect rod as needed and tighten all the necessary screws The threaded hole on the side slot of the rod lines up with
134. ble for mass analysis By a suitable choice of RF DC ratio the filter can be made to discriminate against both high and low mass ions to the desired degree The RF voltage magnitude and frequency determine the mass of the ions that undergo stable trajectories down the filter As the RF amplitude increases heavier ions start to oscillate in phase with the RF and collide with the rods The DC RF ratio determines the filter selectivity As the DC increases at constant RF heavier ions are defocused by the negative DC component The attractive features of the quadrupole as a mass analyzer are evident from the above discussion The quadrupole provides a convenient filter which can be tuned to the desired mass by varying the amplitude of the RF voltage the mass selectivity i e resolution can also be varied electronically by simply adjusting the DC RF ratio Simultaneously varying the amplitude of the DC and RF voltages allows entire mass spectra to be scanned CIS Quadrupole Gas Analyzer 3 12 Quadrupole mass filter Mass Range Resolution and Throughput The most important characteristics of a quadrupole are the mass range its ultimate resolution and its throughput characteristics The mass range is the range of masses defined by the lightest and the heaviest singly charged ions which can be detected by the mass spectrometer The SRS CIS Analyzer is offered in three different models with mass ranges of 1 to 100 CIS100 1 to 200 amu CIS 200
135. ble with the required data acquisition rates A CIS Quadrupole Gas Analyzer 3 20 lon Detector better alternative is to turn on the CDEM and adjust its gain so as to enhance the signal not the noise while keeping the scan speed the same or even faster The CDEM is a very quiet i e low noise amplifier and only starts to contribute to the baseline noise at its higher gains Electron Multiplier upgrades are the most frequent type of hardware enhancement performed by SRS on its entire line of quadrupole mass spectrometers Contact your local representative or Stanford Research Systems for details and pricing CIS Quadrupole Gas Analyzer Pumping System Requirements 3 21 Pumping System Requirements The CIS Probe consists of a quadrupole mass spectrometer equipped with a high conductance differentially pumped CIS ionizer mounted inside a 2 75 Conflat Tee CIS Cover Tee The side port of the CIS Cover Tee i e Pumping System Port provides the connection for the Pumping System required to differentially pump the CIS ionizer and keep the quadrupole mass analyzer filament and detector at high vacuum during process monitoring see Figure 1 for details The ionizer apertures were designed such that during normal operation the pressure in the quadrupole volume can be at least 100x smaller than the pressure in the ionization region Under these conditions a 10 Torr process pressure corresponds to a comfortable 10 Torr pressure on
136. by electron impact directly at the process pressure A pumping system similar to the one used in PPR systems keeps the filament and the rest of the quadrupole assembly at pressures below 10 Torr through differential pumping The design is very simple and was successfully used for many years in gas chromatography mass spectrometry instruments before it was applied in general to quadrupole gas analyzers Advantages of the CIS An understanding of the performance differences between the CIS setup and the more traditional RGA based PPR system is indispensable when trying to choose the sensor setup that 1s best suited for a particular process application A CIS system usually offers several advantages over the OIS PPR Process engineers should carefully weigh those differences before choosing an analyzer configuration for their application Direct sampling The CIS Anode can be viewed as a high conductance tube connected directly to the process chamber The pressure in the ionization area is virtually the same as that in the process chamber The CIS Ionizer produces ions by electron impact directly at process pressure while the rest of the mass analyzer and the filament are kept under high vacuum The electrons emitted by the filament in the high vacuum region enter the high pressure ion formation region through the emission aperture on the side of the anode tube Once formed the ions are extracted for mass analysis through the ion extraction orifice
137. cedure 1 Filament Replacement kit consisting of a set of filaments and spare screws One standard OFHC copper gasket for 2 75 CF Flange New and Clean Precision flat head screwdriver 2 5 mm head Needle nose pliers Latex gloves powder free Clean dust free work area Read all warnings at the beginning of this chapter before attempting to service the probe Set up in advance a clean dust free working area where to carry out this procedure Turn off the CIS and disconnect the ECU from the probe Wait for the probe to cool down for at least 30 minutes after the emission is turned off Severe burns can result if the probe is handled too soon Turn off the pumping system and pressurize the quadrupole chamber to atmospheric pressure levels CIS Quadrupole Gas Analyzer Filament Replacement 7 11 6 Without disconnecting the CIS Cover Tee from the vacuum port remove the six bolts from the feedthru flange at the end of the probe and slide the entire quadrupole assembly out of the vacuum tube Note the rotational orientation of the Feedthru Flange before removing the probe assembly from the vacuum system so that the probe can be reattached in the exact same way it was at the end of the procedure Mark the side of the flanges with a permanent marker if necessary The ionizer the filter and the detector are now fully exposed and easily accessible The alumina seal SRS 7 00787 remains attached to the CIS Port held in place by
138. ch command sequence specifies the command name The rest of the sequence consists of parameters Three types of parameters are allowed numbers asterisk default param and question mark query Not all commands accept all types of parameters and some need no parameters at all In general number parameters can be real or integer however some commands will only accept integers Commands that accept only integers are recognized because the numbers used to specify their parameter range do not include a fractional part The maximum mass number recognized by the CIS Analyzer is model dependent and is represented by M MAX 100 for the CIS100 200 for the CIS200 and 300 for the CIS300 With a few exceptions the data returned by most query commands is a string of ASCII characters terminated by a linefeed lt LF gt decimal ASCII value 10 and a lt CR gt terminator string lt LF gt lt CR gt Ion currents are represented as integers in units of 10 Amps and transmitted directly in Hex format four byte integers 2 s complement format Least Significant Byte first CIS Quadrupole Gas Analyzer 5 28 Initialization Commands Initialization Commands ID INO IN1 IN2 Description Identification query Echo ID string Use to identify the CIS Head connected to the host computer The instrument returns the ID string ASCII format SRSCISHHHIVERT4HISNIHHHHH LEA CR The three string parameters in the exact format sho
139. clock at 172 8 kHz is used to provide heater power to the filament Note that two clocks are required for each cycle so the primary drive current is at 86 4 kHz The switcher s transformer has a 6 1 turns ratio reducing the 24V input to a 4V output which leaves about 3 5V after rectification in the dual Schottky diode D501 The primary of the transformer is operated from the 24VDC supply and is driven differentially by a pair of IRF530 MOSFET s An LT3525 switching controller U501 is used to drive the FET gates The duty cycle of the gate drive depends on the voltage at the COMP pin pin 9 A voltage of about 0 9V or below will set the duty cycle to zero The duty cycle increases to a maximum near 50 for each gate as the voltage on this input is increased to about 3 3V The analog switch U500 controls the source of the signal to the COMP pin If EMIT CTL is low as it is after a reset then the DAC signal EMIT SET is connected directly to the COMP pin allowing for direct control of the filament heater s duty cycle by the CPU This mode is used when the filament is first turned on to verify that the pressure is low enough to allow the filament to remain on When EMIT CTL is set high the COMP pin is connected to the compensation capacitor C500 which will be charged and discharged by the transconductance error amplifier in U501 The error amplifier will compare the EMIT SET voltage or the attenuated EMIT SET voltage
140. commended that the filament be replaced as well during this procedure since some damage is usually inevitable during handling of its fine wire Equipment Procedure 1 Ionizer Replacement kit O100RIC consisting of anode tube filament posts repeller plate extraction plate alumina rings spare screws and e clips and filament replacement kit OTOORFW or O100RFT depending on filament material One standard OFHC copper gasket for 2 75 CF Flange New and Clean Precision flat head screwdriver 2 5 mm head Needle nose pliers Latex gloves powder free Clean dust free work area Read all warnings at the beginning of this chapter before attempting to service the probe Make sure the correct filament spares were ordered with the Ionizer Replacement Kit Set up in advance a clean dust free working area where to carry out this procedure Turn off the CIS Analyzer and disconnect the ECU from the probe Wait for the probe to cool down for at least 30 minutes after the emission is turned off Severe burns can result if the probe is handled too soon Turn off the pumping system and pressurize the quadrupole chamber to atmospheric pressure levels Without disconnecting the CIS Cover Tee from the vacuum port remove the six bolts from the feedthru flange at the end of the probe and slide the entire quadrupole assembly out of the vacuum tube Note the rotational orientation of the Feedthru Flange before removing the probe assembly from
141. ctal 8 bit A D converter counter timers and a multiplexed address data bus to accommodate an external 32Kx8 RAM The ROM is used for program storage the RAM for data storage the EEPROM contains calibration values for the particular unit The power up reset and power fail interrupts are provided to the CPU by U100 a MAX705 Digital UO Ports The microprocessor s I O ports are assigned as follows RTS BUSY CAL_EN LE_DAC18 CS_DAC8 LD_LEDS LD MPX LD MISC A8 15 A0 7 amp DO 7 RXD TXD SPI IN SPI OUT SPI CLK CTS 24 6 RF_CT 5 RF_PRI GND GND FOCUS_I FIL_DUTY FIL_PRI Low indicates that the host computer is ready for RS232 data Low indicates that the 16 bit signal A D converter is busy High enables modification of EEPROM calibration data Set high to latch SPI data into 18 bit RF control D A converter Strobe low to assert CS to octal 8 bit DAC Strobe high to load LED data into output register Strobe high to load multiplexer data into output register Strobe high to load miscellaneous data into output register High address bits for external RAM Multiplexed address and data bits for external RAM RS232 data received from host computer RS232 data transmitted to host computer Serial peripheral interface data from 16 bit A D converter Serial peripheral interface data to 8 and 18 bit D A converters Serial peripheral interface data clock Low to allow host computer to send RS232 data
142. ction Control Name CA CL HV MO NF Description Calibrate All Calibrate Electrometer CDEM s High Voltage Multiplier Option Noise Floor Scan and Measurement Control Name AP HP HS MF MI MR SA SC Description Analog Scan Points Histogram Scan Points Histogram Scan Trigger Final Mass Initial Mass Single mass measurement Steps per amu Analog Scan Trigger Parameter Storage Name MG MV XA XV Description CDEM gain storage CDEM Bias Voltage storage Parameter Address Parameter Value CIS Command List xiii Parameters 9 0 1 2 Parameters 15 105 5 0 1 00 0 1 0 150 Parameters none none 0 2490 0 7 Parameters 0 255 none 1 M_MAX 1 M_MAX 0 M MAX 10 25 0 255 none Parameters 0 0000 2000 0000 0 2490 0 10 0 99999 9999 Echo ID String STATUS Byte Echo STATUS Byte or query response STATUS Byte or query response STATUS Byte or query response STATUS Byte or query response Echo STATUS Byte STATUS Byte STATUS Byte or query response CDEM option Query response Echo Query response Query Response Ion Currents Query response Query response Ion Current Query response Ion Currents Echo Query Response Query Response Query response Query response CIS Quadrupole Gas Analyzer xiv CIS Command List Mass filter control Name ML Tuning Name CE DI DS RI RS
143. culations is that there is a linear relation between the pressure and the corresponding ion current signals of the gases This assumption is only strictly correct as long as the pressures in the CIS Head are kept below ceratin values 10 Torr for RGA Mode and 10 Torr CIS Mode Deviations from linearity are to be expected above the recommended maximum pressure values due to space charge effects in the ionizer and ion neutral scattering interactions in the filter A more thorough check of the sensitivity factors involves measuring the ion signals over several orders of magnitude of partial pressure to determine the range over which a linear relationship exists The sensitivity factor for the gas is calculated as the slope of the signal vs pressure response over the linear range RGA Windows automatically uses partial pressure sensitivity factors stored in the non volatile memory of the instrument s head as conversion factors between the ion currents received from the head and the pressure units selected by the user A Sensitivity Tuning command in the Head menu automates the sensitivity tuning procedure described above and allows the user to recalibrate or change the sensitivity factors very easily The procedure also prompts the user to select the desired mode of operation before the current measurements are performed Consult the RGA Windows User s Manual and the CIS Quadrupole Gas Analyzer Sensitivity Tuning Procedure 6 13 On line He
144. cup and then repeat the same measurement with the electron multiplier without changing anything else The gain of the multiplier is the ratio of the multiplier output current to the Faraday cup output current Note that there is no need to change the sign of the electron multiplier signal prior to the division since the firmware automatically reverses its sign before transmitting the value The CIS Head can store a single set of High Voltage Gain values for the electron multiplier in its non volatile memory RGA Windows uses the voltage value to bias the CDEM and the gain value to divide the ion currents when the CDEM is turned on See the HV MV and MG commands in the CIS Command set for details on the command level implementation of this procedure RGA Windows can automatically program the gain of the electron multiplier for any mass using the automatic Electron Multiplier Gain Adjustment function of the Electron Multiplier command Head Menu Select a gain value between 10 and 1 000 000 choose a mass value for partial pressure measurements and the RGA Windows program automatically calculates the required high voltage setting when the Adjust button of the Electron Multiplier Window is pressed The HV and gain settings are saved into the CIS Head and used every time the CDEM is turned on All data acquired while the CDEM is on gets automatically divided by the gain before it is displayed CIS Quadrupole Gas Analyzer Chapter 7 Maintena
145. d AGA lon er Turbe Pump Signal Figure 2 Two Layouts of Post Aperture Vacuum System The system shown in Figure 1 can be assembled as a simple package Using a small 70 liter s or less hybrid turbo pump and a diaphragm backing pump will eliminate any concern of oil The use of this pump pair also eliminates foreline traps and isolation valves The operation of the system should be simple open the Hi C valve at low pressures or open the sample valve at high pressures SRS Residual Gas Analyzer Appendix B 5 High Pressure Sampling gt 100mbar At high pressure the aperture assembly is insufficient to reduce the pressure while maintaining response time Consider an aperture that reduces the pressure from 10 mbar to 10 mbar when used with a 70 liter s turbo pump The volumetric flowrate on the high pressure side of the aperture would be 7 microliter s Any dead volume on the high pressure side of the aperture Figure 3 would cause a large response time constant te volume flowrate If the aperture had a small dead volume of 1 2 inch of 0 250 OD tube 0 028 wall the time constant would be 35 seconds This is not an acceptable response time 10 mbar Cal volume 10 Smbar Figure 3 Small Dead Volume Slows Process Response time To achieve a fast response time a capillary inlet is used with bypass pumping as shown in Figure 4 The system reduces the pressure in two stages Most of the sampled gas is draw
146. d Parameter error HSparam param 0 255 Description Histogram Scan Trigger Echo Ion Currents Excecute one or multiple Histogram Scans under the present scan conditions The scan parameter can be set for single multiple and continuous scanning operation A Histogram Scan consists of as a succession of individual mass measurements see MR command over a pre specified mass range The mass range for the scan is set in advance with the commands MI Initial Mass and MF Final Mass The type of detector and noise floor settings to be used during the scan must be selected in advance with the NF and HV commands A current value is transmitted for each integer mass value between MI and MF for a total of MF MI 1 measurements See HP command For maximum data throughput ion currents are represented as integers in units of 10 Amps and transmitted directly in hex format four byte integers 2 s complement format Least Significant Byte first Important e Any command received by the CIS Head in the middle of a scan will immediately stop the scan halt transmission and clear the transmit buffer CIS Quadrupole Gas Analyzer 5 42 Scan and Measurement Commands e The detector s zero and the internal scan parameters are checked and corrected at the beginning of each scan resulting in a slight delay before the scan actually starts e An extra current value 4 bytes unrelated to the scan is transmitted out to the host compu
147. d by the user in the field For example removing the screw that fastens the clamp to the HV rod is all that is needed to replace the CDEM Please see the Maintenance chapter for details FC detection is standard in all CIS probes All FC only units can be upgraded to electron multiplier detection without the need to replace the probe See the Upgrading to an Electron Multiplier Detector subsection below for details When the electron multiplier is not turned on multiplier systems operate exactly like the FC only systems The same electrometer is used to measure the ion or electron currents under both detection schemes The ECU automatically connects the necessary electrode to the electrometer depending on the type of detector being used Faraday Cup operation The Faraday Cup FC detector measures the incident ion current directly Positive ions enter the grounded detector strike a metal wall and are neutralized by electron transfer from the metal to the ion The electrons given up in this process establish an electrical current that has the same intensity as the incoming ion current Since the nominal sensitivity of the CIS Analyzer in the CIS Mode is in the order of 10 Amps Torr the currents measured are very small 10 to 10 Amps for pressures in the order of 10 to 10 Torr respectively Minimum detectable partial pressures as low as 10 Torr are possible with the FC in the RGA Mode However in real time applications the FC detect
148. d electron current is achieved The Filament LED is turned on to indicate the presence of emission and the filament s Background Protection Mode is automatically enabled to continuously 675Hz monitor the operation of the filament The conditions detected during Background Filament Protection are e Filament not present burnt or not installed e Unable to set the requested emission current If any of these two error conditions is detected while the filament is on the heater is immediately shut down and the specific problem is reported as follows Bit 1 of STATUS is set FIL_ERR is updated Filament LED is turned off Error LED is turned on The Leak and Burnt LED s are updated according to the specific problem encountered 6 The Electron Multiplier is also turned off rile eas E Once detected a filament error can only be cleared by successfully turning on the filament to a finite electron emission current It is always good practice trying again if the first attempt to get emission failed Please refer to the FL command in the CIS Command Set to get more details on the operation of the filament CIS Quadrupole Gas Analyzer Chapter 9 Circuit Description This chapter describes the electronics circuits located inside the Electronics Control Unit of the CIS Analyzer The same basic electronics are used in the RGA and CIS line of quadrupole mass spectrometers manufactured by Stanford Research Systems There
149. d linearly related to the voltage output of an RF Driver circuit Clearly a linear relation exists between the output of the RF Driver the RF amplitude on the rods and the mass setting of the filter The purpose of a Peak Position Tuning Procedure is to determine the voltages that the RF Driver must output at O and 128 amu so that all the peaks in an analog spectrum appear in the right position The RS command is used to program the voltage output of the RF Driver 128 amu during the Peak Position Tuning Procedure The value is saved in the non volatile memory of the CIS Head and used by the firmware to generate the internal scan parameters used to step the RF during scans and single mass measurements Note to Supervisors A calibration disable jumper JP100 available on the circuit board can be used by a supervisor to block any attempt to modify the value of the DI parameter Supervisors may use this feature to prevent accidental changes in the calibration parameters by inexperienced operators Setting JP100 will disable peak tuning of the Head Parameters RSparam param 600 0000 1600 0000 If Calibration is enabled by the JP100 jumper See CE Command the parameter is saved into the non volatile memory of the CIS Head and the internal scan parameters used to step the RF during scans and single mass measurements are updated accordingly CIS Quadrupole Gas Analyzer 5 64 Tuning Commands RS Use this format to replace the peak tun
150. due to the reduced bandwidth of the electrometer and increased averaging CIS Quadrupole Gas Analyzer Detection Control Commands 5 39 The NF parameter must be chosen keeping in mind the strong interplay between detection limit and acquisition speed Histogram scans analog scans and single mass measurements all share the same value of NF setting during measurements Important The NF parameter is set to its default value when the CIS Analyzer is turned on It is good practice to readjust the Zero of the ion detector every time the electometer s noise floor setting is changed This is particularly important if the new detector settings have not been used in a long time or since the unit was turned on or recalibrated with the CL command See the CA command for details and more recommendations RGA Windows note When using the RGA Windows program to operate the spectrometer the Scan Speed parameter setting available in the Scan Parameter Setups of the Scan menu is used to set the NF parameter value in the CIS Head according to the equation NF ScanSpeed 1 Parameters NFparam param 0 7 The parameter represents the noise floor level desired Lower parameter values correspond to lower baseline noise better detection limits and increased measurement times Please refer to the Electrometer section in the Electronics Control Unit chapter to obtain detailed information about detection limits and bandwidth values as a function of
151. e CIS Quadrupole Gas Analyzer Introduction 4 3 filament electron multiplier electronics system probe and communications and alert the user of any problems CIS Quadrupole Gas Analyzer 4 4 Front Panel Front Panel The ECU mounts directly on the probe s feedthru flange Its front panel is designed to rest flat against the back surface of the probe s flange and it is not visible while the ECU is locked in place Probe alignment holes Clearance holes 6 places Internal connectors Locking screws 2 places Figure 2 ECU Front Panel The front panel of the ECU box has nine holes of three different sizes and two locking screws The big hole in the center provides access to internal connectors that line up with the feedthru connectors of the probe The six equally spaced holes surrounding the big hole provide clearance for the six bolt heads on the back of the probe s feedthru flange The two remaining holes 1 4 diameter line up with the alignment rods of the probe and assure the correct alignment between the ECU and the Probe during installation The locking screws line up with two threaded holes on the back of the feedthru flange and are used to lock the ECU box in place CIS Quadrupole Gas Analyzer Rear Panel 4 5 Rear Panel The rear panel of the standard ECU Box has two connectors two locking knobs a cooling fan and eight LED s Units with the optional built in power module Option 02 also
152. e CIS Analyzer rely on the assumption that there is a linear relationship between the partial pressure and the corresponding ion current signals from the different gases Each gas ionizes differently and its ions make it through the mass filter with different efficiencies As a result the proportionality constant relating the ion current of a gas to its partial pressure is very dependent on the specific gas The partial pressure sensitivity of the CIS analyzer to a gas g Se is defined as the ratio of the change H Ho in principal mass peak height to the corresponding change P Po in total pressure due to a change in partial pressure of the particular gas species Ho and Pj are background values Sg H Ho P Po The units of S g are of ion current per unit pressure amp Torr for example The sensitivity of the instrument changes with time due to aging of the head and is a strong function of the operating conditions of the instrument Careful quantitative analysis requires that the sensitivity factor S g be determined for every gas which may be a component gas in the system being analyzed The sensitivity factors must be obtained under the same operating conditions that will be used during general partial pressure analysis since they depend on many instrumental parameters including ionization energy emission current mass filter setting type of detector etc For example the RGA CIS 70 and CIS 35 modes of operation will use d
153. e Quadrupole Cylindrical rods rod diameter 0 25 rod length 4 5 Detector type Faraday cup FC standard Electron multiplier CDEM optional Resolution per AVS Better than 0 5 amu 10 peak height standard 2 3 Adjustable to constant peak width over the entire mass range Sensitivity A Torr Measured for N 28 amu with 1 amu full peak width 10 height RGA Model 10 FO 10 CDEM User adjustable throughout high voltage range CIS Mode 105 FC Minimum detectable partial pressure RGA Mode CIS Mode Maximum operating pressure Max bakeout temperature without ECU Recommended bakeout temperature CDEM User adjustable throughout high voltage range Measured as the lowest detectable signal at mass 28 with 1mTorr of Argon present 10 Torr FC 10 Torr CDEM 10 Torr FC 10 Torr CDEM 10 Torr to UHV FC 2 10 Torr to UHV CDEM 350 C FC 300 C CDEM 200 C 1l RGA Mode 70eV electron energy 0 5mA electron emission current 8 eV ion energy optimized extraction voltage CIS Mode 70eV electron energy 0 05mA electron emission current 8 eV ion energy optimized extraction voltage CIS Quadrupole Gas Analyzer xii Specifications Ionizer Design Conductance nominal Material Operation Filament Electron energy Ion energy Extraction voltage Electron emission current General Probe dimension Probe mounting flange Pumping system mounting flange
154. e as it was before disassembly before tightening the flange bolts Perform the CDEM Preconditioning steps described in this chapter before using the multiplier for actual measurements Calibrate the gain of the new electron multiplier before using the device for quantitative measurements See instructions in Tuning chapter CIS Quadrupole Gas Analyzer 7 20 Quadrupole filter cleaning Quadrupole filter cleaning The quadrupole mass filter is the heart of the mass spectrometer The sensitivity and resolution of the instrument are ultimately limited by the quality of the quadrupole field between its rods Deposits on the rods accumulate electrostatic charge and distort the field resulting in degraded performance The deposits typically form at the entrance to the mass filter when the analyzer is operated at high pressures or over long periods of time They are often seen as a discoloration of the metal but in some cases i e depending on the residual gas composition they are invisible If contamination of the rods is suspected the first step to take is a one or two day long Probe Bakeout If a bakeout does not eliminate the problem the quadrupole filter will need to be cleaned Note that in order to clean the rods the entire quadrupole head assembly must be taken apart and unless the exact nature of the deposits 1s known the only sure way to remove them will be with a very fine abrasive Warnings e The exact alignment of the rod
155. e emptied all communications are disabled while this happens e Bit 0 of STATUS and RS232 ERR are cleared e A fresh check of the ECU hardware including the 24V P S the Electrometer and the QMF RF P S is performed and the necessary error bytes are updated INI Reset the CIS Head to its factory default settings In addititon to the above the CIS Analyzer is reprogrammed to its default i e Factory preferred values e Default parameter settings are selected for MI 1 MF M MAX SA 10 NF 4 IE 1 EE 70 and VF 50 e The filament s electron emission setting is left unmodified and the ionizer is biased to default voltages if necessary IN2 Activate Standby mode In addition to the above e The filament and the CDEM are turned off Error Checking The command accepts no default or query parameter values The absence of a parameter is treated as a bad parameter error CIS Quadrupole Gas Analyzer 5 30 lonizer Control Commands lonizer Control Commands EEparam param 15 105 Description Electron Energy eV Echo STATUS error byte or query response Setthe Electron Impact Ionization Energy of the ionizer The parameter represents the desired electron ionization energy in units of eV If the filament is emitting electrons at the time the command is invoked the repeller voltage is immediately reconfigured to provide the desired electron energy while the ion energy and electron emission currents
156. e in effective pumping speed at the ionizer cannot be expected increasing the size of the turbo pump Ultimately the effective pumping speed is limited by the 50 Ls conductance of the 1 5 OD piping that connects the CIS probe to the pump As a result as the pressure in the ionization region increases above 1 mTorr the pressure in the quadrupole rises above 10 Torr reducing the lifetime of the filament and the CDEM and increasing the chances of contamination and chemical reactions at the quadrupole The CIS Analyzer can still be operated even at pressures as large as 10 mTorr However the CDEM should not be used and the linearity of the signal will be compromised The use of the CDEM is definitely not recommended for pressures above 2 mTorr CIS Quadrupole Gas Analyzer 3 6 lonizer Note that the signal non linearities we are referring to are for the main components of the gas mixture and do not necessarily affect a composition analysis For example for a sputtering process at 5 mTorr it might not be possible to do an accurate reading of the Ar partial pressure however it is still possible to do a fairly accurate determination of water levels relative to the Ar readings What SRS recommends for measurements of process gases above 1 mTorr is that the ion source inlet be operated under 2 mTorr by the addition of an extra pressure reduction stage For more information on this subject consult the High Pressure Sampling section in the Gener
157. e internal scan parameters MR28 Single measurement triggered 28 amu A single current value is returned and the RF DC are left at 28 3 amu Collect the 4 byte current value returned Use sensitivity factor to convert it to pressure value MRO Turn off the RF DC on the QMF rods when done measuring Single Mass Measurement programming tips e Single mass measurements are very commonly used in program loops where several different masses are monitored in a merry go round fashion and their partial pressures displayed as a function of time e The outputs provided by a set of single mass measurements are often used in process control programs to control alarms analog and digital outputs and relays For example The output of a D A converter can be linearly related to the readings obtained at a certain mass A relay switch can be closed whenever a specific mass concentration goes above a certain level A digital output can be set high when a mass peak goes under a minimum acceptable partial pressure value e For best accuracy of results it is best to perform all consecutive mass measurements in a set with the same type of detector and at the same noise floor NF setting Fixed detector settings eliminate settling time problems in the electrometer and in the CDEM s HV power supply CIS Quadrupole Gas Analyzer Programming the CIS Head 5 21 e Itis good practice to perform an analog scan before triggering a long set of measure
158. e internal scan parameters used by the firmware to step the RF during the scan are checked and corrected at the beginning of the scan to make sure that the correct RF levels i e as specified by the last Peak Tuning procedure are programmed on the RF rods as a function of mass Important e An extra current value in addition to the values corresponding to the mass steps is sent at the end of all analog and histogram scans This extra current value is unrelated to the scan and does not need to be saved or displayed however it CIS Quadrupole Gas Analyzer 5 18 Programming the CIS Head must be taken into account whenever histogram scanning is incorporated into custom software The detector s zero and the internal scan parameters are checked and corrected at the beginning of each scan resulting in a slight delay before the scan actually starts The measurements are performed with the detector that is active at the time the scan is triggered Setting up a histogram scan The following list of commands sets a scanning range of 1 to 50 amu at the slowest scan rate and after checking the number of currents to be transmitted per scan not including extra value transmitted at the end it triggers a single histogram scan Fifty 1on currents and one extra current are transmitted to the computer per scan Each current is 4 bytes long MII Initial mass 1 amu MF50 Final mass 50 amu NFO Slowest scan rate selected HP Histogram Points
159. e obtained and controlled with negative voltages smaller than 2500 Volts in magnitude The sensitivity of the spectrometer increases with the gain of the electron multiplier Higher sensitivities provide lower minimum detectable partial pressures and faster spectral scans Minimum detectable partial pressure limits lower than 10 Torr are possible in the RGA Mode of operation However the increase in sensitivity is obtained at the price of limited dynamic range mass discrimination CIS Quadrupole Gas Analyzer 3 18 lon Detector effects gain instabilities and finite lifetime of the device A good understanding of these limitations is very important to assure accurate quantitative measurements The dynamic range of electron multipliers is determined by their dark current at the low end and by the bias current value at the high end The bias current is established by the external voltage drop along the resistive glass tube and flows along the channel walls replenishing their charge as secondary electrons are emitted Channel electron multipliers operate linearly in the analog mode until the output current is approximately 10 of the bias current The dark current of a multiplier is the electron current measured at its output in the absence of an input ion current The minimum output current that can be accurately measured with the multiplier is equal to the dark current noise Example For a typical resistance of 200 MOhms and a bias volta
160. e output of the internal switching power supply If a voltage out of the allowable range is found the POWER LED is turned off the red Error LED is turned on Bit 6 of STATUS is set and PS_ERR is updated to indicate the specific problem Electrometer STATUS Bit affected 5 Error Byte affected DET_ERR Error Reporting Command ED Error Codes prefix DET CIS Quadrupole Gas Analyzer Built in Hardware Checks 8 11 Power on check Yes Ion currents from the Faraday Cup or the electron multiplier are measured with a very sensitive logarithmic electrometer The voltage levels are digitized with a 16 bit analog to digital converter ADC16 and turned into current values using a digital logarithmic interpolation algorithm that calculate the currents from an internal calibration curve The Electrometer ADC16 system is automatically tested by the firmware on power on and can be checked at any time with the query command ED Several tests are performed during the check 1 The ADC16 input is grounded and its digital output is measured to make sure it corresponds to less than 15 mV 2 A current of 5nA is injected into the electrometer and the output is read and compared to expected values 3 The same test is repeated with 5nA of input current If an error is detected Bit 5 of STATUS is set DET_ERR is updated and the Error LED is turned on The detector is reconfigured to its pre check configuration once the tests are over Quadr
161. e pressure in the gauge may be much higher Long tubulation or other constrictions between the ionizer and the rest of the vacuum system can cause large errors in the partial pressure readings The probe must be protected from evaporation sources that could coat the ionizer Any mounting orientation of the probe itself may be used however keep in mind that enough clearance must be allowed for the Pumping System and the ECU box that are attached to the CIS Probe Choose the orientation of the pumping system prior to the installation of the CIS probe Keep in mind that some of the older turbomolecular pumps can only be operated in a vertical orientation In all cases consult your pump s operation manual before you bolt anything down 5 The following equipment must be available before the installation procedure starts One standard OFHC copper gasket for 2 3 4 CF flange New and clean Six high strength stainless steel bolts for 2 3 4 CF flanges Use 1 4 28 x 1 3 8 bolts with one nut and two washers per screw for flanges with through holes or six 1 4 28 x 7 8 bolts with one washer per screw to attach the probe s flanges to tapped vacuum ports Both standard hex and 12 point bolt heads are compatible with the CIS flanges Silver plated bolts are preferred over messy anti seize lubricants whenever possible Wrenches One or two wrenches will be needed to tighten the bolts and compress the copper gasket Use a 7 16 12 poi
162. e time the sample is in the air lock To keep oxygen out of the main vacuum chamber the air lock is flushed with dry nitrogen then pumped to rough vacuum The flush is repeated two additional times before the sample is finally transferred If this procedure is successful the main vacuum chamber should not be disturbed SRS Residual Gas Analyzer Appendix A 9 mbar Airlock Sequence Cor OST CO Od dO He dS Time Hhrmm ss Figure 4 Airlock Sequence To make these measurements the electron multiplier detector has been used with a gain of 100 which allows all six channels to be recorded every three seconds The standard Faraday cup detector is able to detect these partial pressures but not at this rate The floor channel is set to mass 21 There is rarely anything present at this mass which allows it to be used as an indicator of the minimum detectable partial pressure The sequence starts with the main vacuum chamber at its base pressure of 2 x 10 mbar The chamber is pumped by a turbomolecular pump that is backed by a rotary vane pump A small load lock is attached to the chamber which can be rough pumped by the same mechanical pump and purged with nitrogen At 0 30 the isolation valve between the turbo pump exit and mechanical pump is shut so that the mechanical pump can be used to rough pump the load lock During this time the load lock is repeatedly filled with nitrogen and pumped down Of interest in the data is the ri
163. eck ERROR Byte 24V External P S Electron Multiplier EM a CIS Head component checked Each check involves several tests on the component Bun i 2 Loe b Checks automatically performed upon a power on reset c Error bytes that store the results of the tests for each type of internal check d Error Reporting command that queries the error byte STATUS Error Byte General Status byte Each bit corresponds to a different type of internal check CIS Quadrupole Gas Analyzer 5 66 Error Byte Definitions 7 eessen DET eB Vane VRE PS_ERR Error Byte 24V P S Error Byte 7 ADC 16 Test failure DET7 E DETECT fails to read 5nA input current DET6 5 DETECT fails to read 5 nA input current DET5 rqews 77770700 ES DET ERR Error Byte Electrometer Error Byte CIS Quadrupole Gas Analyzer Error Byte Definitions 5 67 T mssmwemRin Jm em ENLIL M NN RN mw 0 pt mu 00 E QMF ERR Error Byte Quadrupole Mass Filter RF P S Error Byte KEE No Electron Multiplier Option installed EM S E KE Ke Jsed Jsed CEM ERR Error Byte Electron Multiplier Error Byte CIS Quadrupole Gas Analyzer 5 68 Error Byte Definitions ESE LT pee Rr ination 3 Wem enerpesw wom TS rmm SRL ES ESSI Hn KS mr Not used Single filament operation FIL ERR Error Byte Filament Error Byte 7 Not used Parameter conflict Jump
164. ectronics operate from a single 24 2 V DC power supply The peak current requirement is about 2A A universal input 90 264V AC 47 63Hz switching power supply is provided as an option Option 02 so that the system may be operated directly from a line cord CIS Quadrupole Gas Analyzer 9 4 Circuit Description Circuit Description General Description The specifications and features of the many circuits that drive the RGA are determined by characteristics of the quadrupole mass spectrometer such as e the ionizer settings available to the user e the characteristics of the quadrupole mass filter e the magnitude of the ion current levels detected during measurements e an optional electron multiplier The ionizer consists of a dual thoriated iridium filament heated by a current of about 3A at 1 7V The filament and the associated repeller shield are held at a negative potential between 13 and 97V determined by the electron and ion energy settings Vrepeller ion energy electron energy Electrons from the filament are accelerated toward the anode grid cage which is held at a positive potential of 8 low or 12V high The 25 105 eV electrons ionize residual gas molecules in the grid cage The ions are then injected into the mass filter aided by the focus plate which is held at a negative potential of about 90VDC adjustable from 0 to 150V to optimize the throughput of the mass filter and to deflect electrons The ma
165. ectrum analysis Good procedure and strict adherence to them allows a user to infer the integrity of a vacuum system An RGA allows users to prove the integrity of a vacuum system with hard data Further Reading Dawson P H Quadrupole Mass Spectrometry and its Applications American Institute of Physics 1995 Drinkwine M J and Lichtman D Partial Pressure Analyzers and Analysis American Vacuum Society New York Wilson N G Beavis L C Handbook of Vacuum Leak Detection American Vacuum Society New York 1979 SRS Residual Gas Analyzer Appendix B Using SRS RGA s to Sample High Pressure Gasses Introduction The types of analysis performed by an RGA are useful in many applications other than vacuum systems But the RGA is intrinsically a vacuum instrument that operates best under 10 mbar The instruments response becomes non linear above 10 mbar To sample gases at higher pressures a pressure reduction system is needed These systems are basically a restriction and a vacuum pump package Common restrictions are pinholes and capillaries which can provide pressure reductions of more than 6 decades of pressure The vacuum pump package consists of a turbomolecular pump and a backing pump In addition to achieving the desired pressure reduction the design of a system should provide for a fast response and high signal to background ratio At pressures common to vacuum processes a simple aperture based pressure reduction
166. ecuted Since the command execution time can be rather long the CIS Head prompts the end of execution by sending back the value of the STATUS byte to the computer Always check the STATUS Byte value returned for possible errors If one or more bits of the STATUS byte are found set the specific error bytes PS ERR DET ERR QMF ERR CEM ERR FIL ERR and RS232 ERR must be queried individually to diagnose the problem Error diagnosis examples Example 1 The CIS Analyzer is powered up and after the automatic internal checking is over the Power LED is turned off and the Error LED is turned on The problem is immediately diagnosed visually as a failure in the 24V External P S check A multimeter could be used to check the output of the external power supply and determine the nature of the problem however the computer could also be used to diagnose the problem using the query commands The ER query command returns a STATUS Byte with bit 6 set indicating a 24V P S problem The EP query command is then used to query PS ERR Bit 6 of PS ERR is found set Error Code PS6 indicating that the P S output is less than the acceptable minimum of 22 V This error is also immediately reported by the RGA Windows software as an Error Code PS6 and the Troubleshooting section can be consulted to solve the problem Example 2 The CIS Analyzer is idling between scans waiting for commands from the computer when suddenly an inlet valve is acciden
167. ed out to the host computer over RS232 As a result of the high acquisition rate there might be a delay between the time at which the data is collected by the CIS head and the time at which a complete spectrum is displayed by the host computer The time lag between data acquisition and display depends on a large number of factors including the scan rate NF setting the host computer s processing speed and the amount of handshaking CIS Quadrupole Gas Analyzer Programming the CIS Head 5 17 activity over the RS232 lines As computers get faster they will be able to catch up with the data acquisition speeds and this problem will no longer need any consideration e Before a new scan starts the microprocessor checks the instrument s internal memory to make sure that no data from any previous scans is pending to be transmitted If data is still pending the spectrometer must finish transmitting it before the new scan can start This process may result in a delay from the time the scan trigger is received to the time it actually starts Using the SC1 command and waiting until the whole scan data stream is transmitted back to the host computer will minimize the problems that are associated to this feature e Perform a complete Peak Tuning procedure on the CIS Head if the peaks in the spectrum do not appear at their correct mass values Consult the Peak Tuning section in the Tuning chapter for details Setting up Histogram Scans A Histogram Bar
168. eeeeseeeeeenseeeeeeeseeeeeenseeneeseseeeeeseseeeeeseseeneeseseeneesnsseneees 5 13 Setting up Analog Scans sisenes inis enean eaae meaa e e ar EEEren a eaaeo aaa eean pde eaaa PHE enat aui tupakan Eni 5 15 Setting up Histogram Scans eese eiieeeeeeeeeenn seen nnnm nain tn nasa nnne nnn ennnen nanne 5 17 Single Mass Measurements e eieeeeeiesesiees seen eee ee nnne nn san nnnm nn nn nnn santa sas nnne sn Rasa nasi 5 19 Storing information in the CIS Head eese eeenee enne ennt nn snnt ennnen ann 5 21 Programming the Quadrupole Mass Filter eeeeeesesee eene eene nnns 5 22 Error Checking the CIS Analyzer eeeeeesieeseseeeeeeeeeeeee seen enne nennt nina sana nennt nnns 5 23 GIS Command Set siirinsesi 5 27 Initialization Commands liie reet cerea eaae pa EEN SEN 5 28 CIS Quadrupole Gas Analyzer 5 2 Programming the CIS Head IR EE 5 28 TINO TN IC 5 28 lonizer Control Comman0ds er eeee cesses ese eene nene NEEN asa nasa sa snas anam asa sa sa nasa sna Ds sas 5 30 EEp tam param 15 105 T 3 esee me dee Ue pee eee ler e E rere eee 5 30 EL param param 0 00 3 50 75 7 e ete eter ca a eerte ede eto nde EE 5 30 IEparam param Onl 5 3 E 5 32 MRparam patam 0 130 5 P elenen testi tp indere ERREUR RH Ip Lr HERR Hec ep n Eeeh 5 33 Detection Contro
169. eeeeseeesesneeeeeeeescaeseseeeenseaeeeeeeeseaeseseenenseaeees 5 55 SU Rt ETT M E E 5 55 lb 5 55 EI c ET Rm E M RE 5 56 EM ne steer ER street ee RV ea ab oe ene ete Eee a eligi ee DNO 5 56 Ep oce pu qa LL Ei LEE pen EE 5 57 EL RE 5 57 ER Aeneane Mee IM 5 58 Tuning Commands 3 2 i eet nt ate ee ne ened dates vt petra aa 5 59 SE osse aen teeth tein itenim rem PEPER A eed 5 59 Dipara par m 0 255 5 2 nes Ree rrt eee e Ye e Re vr C Eee ges 5 59 DSparam param 0 8500 40 8500 5 5 60 RIparam param 86 0000 86 0000 none 5 61 RSparam param 600 0000 1600 0000 none sssseeseeeerenenee enne 5 63 Error Byte Detinitlons riui Dein ee eid eee eel 5 65 CIS Quadrupole Gas Analyzer Introduction 5 3 Introduction The CIS Analyzer comes standard with an RS232 communications port A host computer interfaced to the instrument can easily configure calibrate diagnose and operate the quadrupole mass spectrometer using simple ASCII commands The CIS head executes the commands in the order received and when information is requested data is quickly returned to the computer for analysis and display The fast exchange of data between the host computer and the CIS Analyzer provides dynamic information about the status of a vacuum process or system The Command Set facilitates integration of all the spectrometer functions into any processing or diagnostic program The RGA COM Utility Intoduction The RGA
170. ence of the CDEM is reported setting bit 7 of CEM ERR before the byte value is transmitted In all cases the CEM ERR byte value is sent to the computer in ASCII format with a lt LF gt lt CR gt terminator CEM ERR and Bit 3 of STATUS are then cleared This query command can be used to determine whether the CDEM option is installed in the CIS Head being programmed A CDEM option is available if Bit 7 of CEM ERR is cleared when the byte is queried See also MO command CIS Quadrupole Gas Analyzer EP EQ Error Reporting Commands 55 57 Parameters This command is a query and can only have one parameter format EM Error checking The only acceptable parameter is a question mark The absence of a parameter i e EM is treated as a bad parameter error Description PS ERR Byte Query Echo PS ERR Byte Query the value of PS ERR and update its value after running a fresh check on the 24V External Power Supply Bit6 of STATUS and the PS ERR byte are updated based on the tests results The PS ERR byte value is returned to the computer in ASCII format and with a lt LF gt lt CR gt terminator No errors are present as long as the byte value is zero Consult the Error Byte Definitions section of this chapter for detatils on the different error bytes of the CIS Analyzer Consult the Troubleshooting chapter of this manual for possible causes and solutions to any problems reported Always try the query a second time bef
171. ent Positively biased grid cage of the ionizer within which the ionization of the gas molecules takes place Note In the SRS RGA the voltage bias of the anode grid in Volts sets the ion energy in eV for the spectrometer Atomic mass unit abbreviation amu A unit of mass equal to one twelfth the mass of a neutral carbon atom having six protons and six neutrons C equivalent to 1 660566 10 kg Background signal H Output signal measured with respect to baseline which is obtained before the introduction of any gas in the chamber Base pressure also Background pressure Total pressure before introduction of any gases into a vacuum system Usually the base pressure is the lowest pressure that is typically achieved in the vacuum chamber Baseline The output signal from the RGA when no ions are arriving at the detector CDEM Abbreviation for the type of electron multipliers known as Continuous Dynode Electron Multiplier CF Abbreviation for Conflat type flange CF Nipple A short section of vacuum pipe terminated with a standard Conflat flange connector at each end Charge Q The electron charge of an ion Ion charge occurs in multiples of the electron charge e Drift A change in time in the avearge output signal at constant partial pressure SRS Quadrupole Gas Analyzers 2 Glossary of Terms ECU Abbreviation for electronics control unit Electron emission The release of electrons from the heated filament
172. ent of cleaning procedures While the TCE successfully removed the oil the vacuum chamber was left more contaminated than it SRS Residual Gas Analyzer Appendix A 7 would have been without the cleaning The mass spectrum provides a more accurate evaluation of cleaning procedures than pump down time and base pressure Just because a system pumps down quickly does not guarantee that undesirable contaminants have been eliminated The large dynamic range of the RGA also allows evaluations to be made more quickly After a vacuum system has been brought up to atmospheric pressure it will require an extended period to pump back down to its ultimate vacuum If the vacuum system does not quickly reach its ultimate vacuum the next step is commonly a high temperature bakeout If the vacuum system has still not reached its ultimate vacuum problems are suspected and typically a leak tester would be attached to the system With the RGA the user does not have to wait several hours for the water to pump down or perform a bakeout before determining if a system is contaminated The RGA can make measurements as soon as the total pressure reaches 10 mbar The large dynamic range will allow impurities to be seen at 10 mbar or leak testing to be performed in the presence of a this high total pressure Thereby the RGA allows a great reduction in turn around time after a vacuum system has been brought up to atmosphere SRS Residual Gas Analyzer 8 Append
173. ential and is different for every molecule Above the threshold the ionization efficiency increases linearly with the electron energy until a maximum is reached For most molecules this maximum is in the range of about 50 100 eV and for electron energies above the maximum the ionization efficiency slowly decreases with electron energy The minimum electron energy required to doubly ionize a gas molecule i e to generate a doubly charged ion is always larger than the energy required to remove a single electron from the same molecule This property of the ionization potentials is used in the CIS Analyzer to eliminate spectral background interferences For example while looking for water impurities in Ar sputtering processes 35 eV electrons are often used in the CIS Mode of operation to eliminate the Ar peak 350 ppm for 70 eV electrons CIS Quadrupole Gas Analyzer lonizer 3 7 that interferes with water detection at 18 amu This mode of operation referred to as CIS 35 is so commonly used that itis standard menu option in the RGA Windows software The Kinetic energy of the ions as they move down the ion filter simply referred to as the ion energy and expressed in eV is equal to the voltage biasing of the anode tube Two ion energy settings i e anode voltages are 4 low or 8 eV high The ion energy setting affects the magnitude of the ion signals collected i e sensitivity of the spectrometer and limits the ultimate resolutio
174. er 3 3 lonizer The type of ionizer used in the CIS Analyzers is referred to as a closed ion source CIS Positive ions are produced in the ionizer by bombarding gas molecules with electrons derived from a heated filament The ions are then directed toward the entrance of the ion filter where they are separated based on their mass to charge ratio Description The CIS sits on top of the quadrupole mass filter and is simply a short gas tight tube with two very small openings for the entrance of electrons and the exit of ions The source is exposed to the process environment 10 mTorr and ions are produced by electron impact directly at the process pressure Electrons enter the ionizing region through an entrance slit of dimensions 0 190 x 0 025 The ions are formed close to and attracted by a single extraction plate and exit the ionizer through a circular aperture of 0 062 diameter centered on the quadrupole axis Alumina rings seal the tube from the rest of the QMS and provide electrical insulation for the biased electrodes A pumping system attached to the Pumping System Port of the CIS Cover Tee keeps the filament and the rest of the quadrupole mass spectrometer at pressures below 10 Torr through differential pumping The closed design of the ionizer enhances the signal from the sample gas relative to the signals arising from the background gases present in the analyzer and is directly responsible for the sub ppm detectability limits t
175. er conditions Sensitivity factors change as a factor of time due to aging and periodic recalibration is necessary The gain of the electron multiplier is mass dependent and needs to be determined prior to performing measurements with the device The gain characteristics of the multiplier change with time and periodic recalibrations are very important The following sections of this chapter describe several tuning procedures designed to assure that all the calibration conditions described above are satisfied prior to a set of partial pressure measurements All tuning procedures can be executed from RGA Windows using a set of Tuning Commands built into the program The On line Help files provide all the information necessary to set up and execute the tuning commands Users writing their own programs can implement the procedures themselves using the CIS Command Set and the instructions of this chapter All tuning procedures require the ability to introduce pure gases or a mixture of gases of known composition into the vacuum system and a way to measure or calculate pressures Auxiliary calibrated pressure gauges are required to measure the pressure of the calibration gases Most gauges that perform indirect pressure measurements are calibrated for a single gas N gt or Ar and a table of conversion factors will be needed to convert the readings for other gases When only a few choices of calibration gases are available choose those that are most l
176. er dapp EL 1 2 Before You Open the BOx 2 een SEENEN 1 2 ir dd D 1 2 Standard Equipment Supplies 1 2 DEER SCHEIER 1i ike AIO e ehe EE HERR ERR EC ERR Ee pa bbs eR M LUN REEL Fea abc eee CERE AE 1 3 Optional Equipment i eR eR edes 1 3 EU Lu Le TL 1 4 tree Dt Le pe LEE c EE 1 4 Pressure Reducing Gas Inlet System eeeeeeeeeeisesseeseeeneeen nennen nnne tnter nnn 1 4 Probe Installation ee 1 5 Hardware R quirements 4 ego eR ER aye a tuetur 1 5 Procedu EE 1 7 Pumping System Installation eeeeeeeee eiie einen ee nneeee nenne natnm nnn nn nnn na snnm annt n nnn 1 7 Electronics Control Unit Installation eeeeeeeeee eren eese eene nnne nennen tnnt nnn 1 8 Hardware Requirements e cies meti peccet rt eee t eet Ue rhet cedet ita 1 8 Proced te 2 5 uendere Ee 1 10 RGA Windows Installation eeeeeeeeeeeeiee sisse seen e nennen nnns nnn natn nhan nhan inane sinn ne tn nana 1 11 Minimum System Requirements Single Head Operation see 1 11 Procedu te onn bee ea tee e vere pe tee vi e n eee ve e a Eee RE MEN ede 1 12 Turning on the CIS Analyzer eeeeseeeeeeeeeeee nennen nnne niiae nasa iaiaaeaia assa san nasa nnns 1 12 Running the CIS Quadrupole Gas Analyzer
177. er protection violation Transmit buffer overwrite OVERWRITE in receiving Command too long Bad Parameter received Bad command received RS232 ERR Error Byte Communications Error Byte CIS Quadrupole Gas Analyzer Chapter 6 Tuning This chapter describes the tuning procedures needed to calibrate the CIS head and assure accurate qualitative and quantitative measurements WARNING The Tuning procedures described in this chapter should be performed by qualified personnel only A mistuned CIS Head will provide Erroneous Readings until it is properly retuned In This Chapter Iottod ugin eegen 6 2 DEI rm 6 3 Peak Tuning Procedure ssecceceseeeeeseeeeeeeseseeeeesenneeeesenneeeeseneenensenneeseseneeesesenneeseseneeeesseneeeseseeneesnseeseees 6 4 niai e 6 4 General Procedure 5 reir ra ara ENEE EES 6 5 Peak Position Tuning Algorithms eeeeeeeeeeeeeeeenee enne enne nnne nnne nnne nenne nnn nnn 6 6 Peak Width Tuning Algorithms eeeeeee eese nnmnnn nnmnnn annn 6 8 Temperature effects on the mass scale calibration eene 6 9 Sensitivity Tuning Procedure eesiieesieeeeeieeeeees eee ne nenne ninth ania natnm ase tn nasa snas stans nnns ann nasa a 6 11 Electron Multiplier
178. er the same pressure conditions brings the detection limits under IO TT Torr providing a cleaner baseline better suited for the analysis of the residual gas composition and the detection of small leaks Example 2 A common application of the CIS Analyzer in the CIS Mode of operation is to monitor trace impurities in a gas phase process The ionizer is typically exposed to the high purity gas in the mTorr range and sub ppm 10 Torr impurities are often monitored Partial pressure detection limits for FC detection in the CIS Mode are in the order of 10 Torr That corresponds to a 10ppm detection limt for common impurities With the help of the CDEM gain the partial pressure detection limit can be reduced down to 10 Torr or better which brings the detection limits down to the sub ppm levels that are often required Example 3 CDEM detection can dramatically increase data throughput when speed is an important issue in the partial pressure analysis There are two fundamental ways to increase the signal to noise ratio of any measurement One way is to reduce the baseline noise while keeping the signal at the same level Another way is to amplify the signal while keeping the baseline the same Scanning at a lower scan speed provides increased averaging and a reduction of the baseline noise while keeping the signal levels untouched However it also slows down the measurements and can result in a reduced data throughput that might not be compati
179. erating mode of the instrument Careful quantitative analysis requires that the sensitivity factor S g be determined for every gas which may be a component gas in the system being analyzed The sensitivity factors must be obtained under the same operating conditions that will be used during general partial pressure analysis since they depend on many instrumental parameters including ionization energy emission current mass filter setting type of detector etc For example the RGA CIS 70 and CIS 35 modes of operation will all have different sensitivity factors for the same gas since they correspond to three different sets of ionizer conditions In order to separate the gain of the electron multiplier from the intrinsic sensitivity of the CIS head the sensitivity factors of the CIS Analyzer are defined for Faraday Cup detection A separate Electron Multiplier Gain Factor is used to correct the ion signals when the electron multiplier is turned on See the Sensitivity and Electron Multiplier Tuning sections of the Tuning Chapter for details The basic procedure for determining the sensitivity of a particular gas in the CIS Analyzer is the following CIS Quadrupole Gas Analyzer 2 16 Partial Pressure Analysis Basics Introduce the pure gas into the vacuum system at a known or calculable pressure typically around 10 Torr e Measure the output signal from the CIS for the principal mass peak of that gas using the Faraday cup detect
180. erent sources including hardware communications probe i e bad filament and operating environment i e overpressure Troubleshooting is simplified by an assortment of diagnostic commands built into the firmware and fully supported by the RGA Windows program Leak The Leak LED is automatically turned on whenever the filament heater is unable to establish a requested emission current The most common reason for this problem is a serious leak in the vacuum system In the event of an overpressure detection the filament emission and the electron multiplier are immediately turned off and the Error and Leak LED s are turned on to indicate the problem Important The Leak LED will also be turned on if the filament is excessively worn down or damaged However this is a more rare event due to the long life of the filaments Burnt The Burnt LED is turned on whenever the ECU fails to detect a filament A burnt or missing filament are possible sources for this problem The Error LED is also turned on to clearly signal the presence of a filament error CIS Quadrupole Gas Analyzer Electrometer 4 9 Electrometer Detection limit vs scan rate A unique temperature compensated logarithmic picoammeter built into the ECU box measures the ion currents collected by the Faraday cup FC or electron multiplier CDEM The output voltage of the electrometer is equal to the logarithm of the ion current so that several decades of signal can be read on
181. ers Eventually the gain drops to unacceptable values and the multiplier needs to be replaced As a rule of thumb the CDEM should be replaced when the required gains can no longer be achieved by increasing the bias voltage Warnings The CDEM is very delicate and should be handled with extreme care Handling and mounting of the CDEM should only be performed in a clean vacuum fashion Work ona clean dust free area Avoid dust lint and any kind of particulate matter Wear talc free rubber gloves or finger cots Use properly degreased tools Avoid excessive shock such as from dropping onto a hard surface Remember that the CDEM is made out of glass Use only SRS supplied electron multipliers for replacement Equipment e Multiplier Replacement kit consisting of new CDEM with mounting clamp in place and spare screws e One standard OFHC copper gasket for 2 75 CF Flange New and Clean e Precision flat head screwdriver 2 5mm head e Needle nose pliers e Latex gloves powder free e Clean dust free work area Procedure 1 Read all warnings at the beginning of this chapter before attempting to service the probe 2 Setup in advance a clean dust free working area where to carry out this procedure 3 Turn off the instrument and disconnect the ECU from the probe 4 Wait for the probe to cool down for at least 30 minutes after the emission is turned off Severe burns can result if the probe is handled too soon CI
182. es Use the power entry module on the back panel of the ECU box to power the CIS Analyzer directly from an AC outlet Use the three wire power cord provided by SRS to connect the CIS Analyzer directly to a properly grounded wall outlet ECU RS 232 connection Use the straight through RS232 cable with 9 pin type D connectors to connect the computer usually DTE to the CIS Analyzer Insert the 9 pin Type D male cable connector into the ECU connector marked RS232 DCE 28 8k on the back panel of the ECU box Insert the 9 pin Type D female cable connector into the RS232 port on the computer Use the DB25 to DB9 connector adapter if the computer has a 25 pin Type D connector RGA Windows Installation The RGA Windows Software is preinstalled at the factory in CIS Analyzer systems that include the optional Computer system option O100CS Minimum System Requirements Single Head Operation IBM compatible 486 CPU machine at 66 MHz with 8 Mbytes of RAM or greater Mouse or equivalent pointing device Serial port 16550 UART recommended but not necessary Straight through DB 9 to DB 9 RS 232 cable 5 Mbytes of free hard disk space for RGA installation and runtime use 1 44Mbyte 3 5 floppy drive for the installation disks Super VGA graphics card running in 800x600 256 color mode A sound card if the audio features are needed Microsoft Windows version 3 1 or later CIS Quadrupole Gas Analyzer 1 12 Installation Note The RGA pro
183. es one power cord O100RFW Replacement Tungsten Filament for CIS pkg of 5 filaments O100RFT Replacement Thoriated Iridium Filament for CIS pkg of 2 filaments O100EM Replacement Electron Multiplier O100RIC Replacement Ionizer Kit includes filament for CIS O100TR Computer output card cable relay card O100TS Computer output card TTL screw terminal card O100CS Computer system IBM compatible PC with factory installed RGA Windows software O100RM 19 Rack Mount enclosure for computer and monitor O100BV Bypass Valve assembly with pressure reduction orifice 2 75 CF Flanges O100TDP Turbomolecular pump with 2 75 CF Flange and Diaphragm Pump CIS Quadrupole Gas Analyzer 1 4 Installation Installation Introduction A complete SRS CIS Analyzer system consists of 1 Pressure Reducing Gas Inlet System for operation above 2 mTorr 2 CIS Probe 3 Pumping system 4 Electronics Control Unit ECU 5 RGA Windows Software Specific hardware requirements and installation instructions are needed for each one of the components Important e Follow the installation steps in the strict order in which they are presented in this chapter e Do not power up the instrument until it is indicated in the procedure e Read the hardware requirements before installation begins Do not start the installation procedure until all requirements are met e Please read and follow all installation instructions to insure tha
184. esignated component of a gaseous mixture within a system as it is exerted on the chamber walls The sum of the partial pressures of all the kinds of gases gives the total pressure Partial Pressure Analyzer abbreviation PPA A compact mass spectrometer used to analyze the residual gas composition in a vacuum system Peak height also peak intensity The maximum ion signal developed in the RGA for a given mass to charge ratio peak SRS Quadrupole Gas Analyzers Glossary of Terms 5 Peak width AM The difference between the mass to charge ratio values on either side of a mass peak at which the signal has dropped to v of the peak height H See also Resolution Principal mass peak The most intense peak in the fragmentation pattern of any molecule Probe also RGA Probe Quadrupole mass spectrometer sensor consisting of an ionizer a mass analyzer and a detector Farday cup or optional electron multiplier Repeller Ionizer Component The repeller grid cage completely encloses the ionizer is biased negative relative to the filament and prevents the loss of electrons from the ion source Residual Gas Analyzer abbreviation RGA A compact mass spectrometer used to analyze the residual gas composition in a vacuum system same as Partial Pressure Analyzer Resolution or Absolute Resolution AM o4 The width AM of the pass band of the filter defined as the full width at which the ion current falls down to 10 of the maximum
185. esolution values of about 0 9 amu amu Also note a 20 amu peak in the low mass spectrum corresponding to TA at 20 i e 40 2 amu Low Mass High Mass L iy 15 16 17 18 19 20 21 22 23 24 25 80 81 82 83 84 85 86 87 88 89 90 amu e amu e Users writing their own computer code can write Peak Tuning Commands for their own programs using the Tuning Commands of the CIS Command Set and the instructions of the following two sections Peak Position Tuning Algorithms The magnitude of the RF determines the mass to charge ratio of the ions that can pass through a quadrupole mass filter without striking the rods i e with stable oscillations A linear relationship between mass and RF amplitude is one of the most attractive features of these type of filters The regulated output of the RF source that powers the CIS Analyzer s quadruple rods is controlled by and linearly related to the voltage output of an RF Driver circuit The RF Driver uses an 18 bit digital to analog converter and some additional electronics to program its output voltages The purpose of the Peak Position Tuning Procedure is to determine the voltages that the RF Driver must output at 0 and 128 amu so that all the peaks in an analog spectrum CIS Quadrupole Gas Analyzer Peak Tuning Procedure 6 7 appear at the right place in the mass axis The calibrated voltage settings in mV are sa
186. est accuracy of results it is best to perform the consecutive mass measurements in a set with the same type of detector and at the same noise floor NF setting Fixed detector settings eliminate settling time problems in the electrometer and in the CDEM s HV power supply e Itis good practice to perform an analog scan before triggering a long set of measurements to assure the correct tuning i e correct peak locations and widths of the quadrupole mass filter Perform a complete Peak Tuning Procedure as described in the Tuning chapter of this manual if shifts in the peak locations are observed e The RF DC voltages are left on at the end of a single mass measurement Use the MRO command at the end of a set of measurements and before quitting a program to make sure the RF DC voltages are left off SAparam param 10 25 Description Steps per amu of analog scan Echo Query Response Set the number of steps excecuted per amu of analog scan The parameter specifies the number of steps per amu During an analog scan the quadrupole mass filter is stepped at fixed mass increments through the mass range specified by the MI and MF commands An ion current is measured after each step and transmitted to the host computer over RS232 SA programs the number of steps excecuted by the CIS Head per amu of analog scan The fixed mass increment corresponding to each analog scan step is equal to the inverse of the SA parameter value Since the CIS A
187. et pointing to a quadrupole mass filter problem The command EQ is used to read in the QMF ERR byte Bit 7 is found set indicating that the RF driver is unable to set the maximum RF value available to the quadrupole mass filter Error code RF7 in Troubleshooting Chapter A quick visual inspection of the CIS head shows that the ECU is not pushed all the way into the probe and no actual connection exists between the rods and the RF driver This error is also immediately reported by the RGA Windows software as Error Code RF7 and the Troubleshooting section can be consulted to solve the problem Example 4 The user notes that the Error LED flashes every time the ID command is sent to the CIS Head and the ID string is never returned i e receive timeout The STATUS byte returned by the ER command has the bit 0 set as expected for a communications problem The specific communications problem is diagnosed using the EC command Bit 0 of RS232 ERR is found set indicating that a bad command is being detected by the CIS Analyzer The user checks the communications program and finds out that due to a typing error the IM string is being sent instead of ID The problem is easily corrected Error Checking Programming tips e Keep a close eye on the Error LED s while programming the CIS Analyzer Diagnose problems as soon as they are detected e Even though a lot of internal checks are performed by the microprocessor not all possible internal erro
188. etting the RF and DC values such that only the ions of interest have stable trajectories down the quadrupole rod assembly By simultaneously varying the amplitude of the DC and RF voltages an entire mass spectrum can be scanned The CIS Analyzer is completely calibrated at the factory so that the ECU automatically programs the RF and DC voltages on the rods to the necessary levels during scans or individual mass measurements The calibration parameters can be accessed and modified by the user in case recalibration or a change in resolution is required Please see the Tuning chapter for details The quadrupole mass filter must be operated in a vacuum Linear operation can be expected up to pressures of the order of 10 Torr In general quadrupoles can be operated at relatively high pressures compared to other types of analyzers The upper limit of useful operation is determined by the collisions between the ions and the neutral CIS Quadrupole Gas Analyzer Quadrupole mass filter 3 11 gas molecules In order to avoid collisional scattering it is necessary to maximize the mean free path of the ions The 100X pressure reduction between the CIS Ionizer and the quadrupole assembly is what makes the quadrupole filter compatible with ionizer pressures as large as 10 mTorr The general principle of operation of the filter can be visualized qualitatively in the following terms One rod pair X Z plane is connected to a positive DC voltage upon which a s
189. ffset correction factors for all the possible combinations of detector settings CIS Quadrupole Gas Analyzer 5 14 Programming the CIS Head can be generated and accumulated in the instrument s memory However all offset correction factors are cleared after a recalibration CL of the electrometer is performed and when the unit is turned off Please consult the CIS Command Set section for details on the CA and CL commands Detector Programming example The following list of commands starts by checking the CIS head to make sure there is a multiplier installed A CDEM is present if a 1 lt LF gt lt CR gt response is sent back to the computer After the test and assuming the CDEM option was detected a voltage of 1400V is set across the multiplier and the noise floor setting is programmed for minimum averaging and maximum scan rate The detector is now fully configured for CDEM measurements with 1400 V of CDEM bias voltage MO Multiplier Option Query Check query response 1 lt LF gt lt CR gt confirms CDEM option HV1400 High Voltage CDEM 1400V Echoes the STATUS Byte NF7 Noise Floor 7 Echoes the STATUS Byte Notes Append a CA command at the end of this list to readjust the zero of the ion detector measurements under the present detector settings The correction factor will then be used by all measurements i e single mass under this same detector settings to correct against zero drifts Use the HVO command to go back to F
190. filament s heater until the requested electron current is established A null parameter value turns off the filament and grounds the ionizer s repeller and extraction plates Command excecution times vary depending on the pre existing ionizer conditions The end of the command excecution is prompted to the host computer sending out the STATUS byte over RS232 The Filament LED reflects the ionizer s emission status at all times A firmware driven Filament Protection Mode monitors the performance of the filament while it is emitting electrons and if a problem is detected at any time the heater is immediately shut down and the problem is reported through the error bytes and the error LED s see below WARNING The pressure in the process chamber must be under 102 Torr before turning the filament on Important The repeller and extraction plates are only biased while the filament is emitting electrons e In order to protect the filament the emission current is defaulted to zero when the CIS Analyzer is turned on e The CDEM is turned off by any overpressure that also shuts down the filament Parameters FL0 00 The filament is turned off and the repeller and the extraction plates are grounded FLparam param 0 02 3 50 The parameter is the requested Electron Emission Current in units of mA The repeller and extraction plates are biased and the filament s heater is activated until the requested electron emission curren
191. gain improvement after the cleaning Warning Stanford Research Systems does not guarantee that this procedure will improve the performance of the CDEM Use this method as a last resort only Materials e Ultrasonic cleaner e Isopropyl alcohol Electronic grade or better e 1000 mL beaker e Oil free dry nitrogen e Petri dish e Clean oven higher than 100 C setting Warning The fumes from isopropyl alcohol can be dangerous to health if inhaled and are highly flammable Work in well ventilated areas and away from flames Warning Read and follow all directions and warnings of the ultrasonic cleaner regarding the use of organic solvents for cleaning Procedure 1 Fill the 1000mL beaker with isopropyl alcohol 2 Gently place the CDEM into the alcohol 3 Insert the beaker containing the CDEM into the ultrasonic cleaner for 10 minutes 4 Remove the CDEM from the isopropyl alcohol and allow it to drain for a few minutes 5 Depending on the contamination level repeat steps 1 4 as needed 6 Blow dry the CDEM with oil free dry nitrogen 7 Place the CDEM in a clean Petri dish and dry at 100 C for about one hour CIS Quadrupole Gas Analyzer CDEM Replacement 7 17 CDEM Replacement There is no need to send the CIS Probe back to the factory for this service The replacement procedure is very simple and can be completed in a few minutes by qualified personnel Gain degradation limits the lifetime of all electron multipli
192. ge of 2000V the bias current is 10 Amps and the output current must be kept under 1 Amp Since the gain at that voltage is roughly 10 the maximum input current at which the output current behaves linearly is 10 Amps 1 Amp 105 Typical dark currents are lower than 10 Amp and the minimum input current that can be detected is 10 Amps Fora sensitivity of 10 Amp Torr this corresponds to an lower and upper limits of 107 and 10 Torr respectively and 7 orders of magnitude of dynamic range The total gain of electron multipliers varies as a function of the mass of the incident ions As a rule of thumb and for small molecules the gain decreases as mass increases This mass discrimination effect is caused by the dependence of ion electron conversion efficiencies on the velocities of the ions entering the detector For example an inverse relationship with the square root of the mass has been reported for monoatomic ions of the same energy For accurate quantitative measurements it is essential to calibrate in advance the gain of the multiplier for the specific ionic species being detected An important problem when working with multipliers is that their gain changes with time Gain degradation is unavoidable and particularly serious just after the detector has been exposed to air or after high quantities of reactive gases have been introduced into the vacuum system The increased surface area provided by the extra channels in the multi c
193. ged ions For example nitrogen is said to have a mass 28 peak Mass Range The range of mass numbers defined by the mass number of the lightest and the heaviest singly charged ions which can be detected by the RGA Mass spectrometer An instrument which produces a beam of molecular ions from a sample separates the resulting mixture of ions according to their mass to charge ratios and provides output signals which are measures of the realtive abundances of the ionic species present Mass spectrum A graph of ion abundance vs mass to charge ratio Minimum Detectable Partial Pressure change MDPP The partial pressure change corresponding to the smallest signal change which can be distinguished from noise A common prescription is Apmin O Sg where o is the noise and S is the partial pressure sensitivity for the gas being measured Noise Random fluctuation in the output signal unrelated to a change in the partial pressure of the gas from which the signal is derived The appropriate measure of noise is the standard deviation On of N independent determinations of the average output signal obtained at constant partial pressure Open Ion Source Also Nude Ion Source An ionizer with electrodes of high transparency to gases Outgassing The evolution of gas molecules from the internal wall surfaces of the vacuum system Parent ion An ion of the same mass as that of the original parent molecule Partial Pressure The pressure of a d
194. gen levels approximately 5 times lower This corresponds to MDPP levels of better than 20 PPM for 28 amu and 4 PPM for 32 amu However the MDPP levels at 28 amu are also affected by the CO contribution from the OIS filament Other sources of background interference are contamination from pump oil backstreaming into the RGA chamber in systems that use conventional oil based roughing pumps Hydrogen is usually impossible to detect at PPM levels because it outgasses readily from the analyzer A gold coated or platinum clad OIS can help in this case Process Gas Interference The other limitation to PPM detection levels in a typical RGA based PPR system is caused by interference from the same process gases that are being analyzed The best way to illustrate this point is to go back to the example of water analysis in the 10 mTorr Ar sputtering process We saw that detecting water at better than 20 PPM levels is very difficult unless the PPR chamber is very carefully baked out and protected from water contamination However as we will see this is only part of the problem there is also a serious interference at m e 18 from the same Ar used in the sputtering system The isotope 6 Ar is present at 0 34 In the electron ionization process doubly charged argon is formed leading to peaks at m e 20 Ar and m e 18 CATH For 70 eV electron impact energy a typical level of Ar is 350 PPM So if you want to detect PPM levels of water in an Ar b
195. gh Voltage power supply is limited to a 2500V output Typical operating range is 1100 2500V In general the lower the average signal current drawn from the detector and the lower the operating voltage the longer the lifetime that will be realized Initial pump down To best maintain the high gain and low dark current properties of electron multipliers it is very important to follow the steps described in the CDEM Pre conditioning section of this chapter during the initial pump down of the electron multiplier The procedure serves to degas the detector and stabilize the gain Failure to follow the recommended steps before powering up the multiplier might result in gain degradation by as much as a factor of ten Contamination The active surface of the CDEM can be repeatedly exposed to air without degradation however it should not be contaminated with dust lint or other particles Organic CIS Quadrupole Gas Analyzer 7 14 CDEN Handling and Care substances present in the vacuum system tend to accumulate on the active surface of the multiplier and lead to slow performance degradation due to reduced secondary emission efficiency Oil contamination is a serious problem and can result in catastrophic destruction of the multiplier use liquid nitrogen traps with diffusion pumps particularly for slicone oil based pumps and molecular sieves traps with mechanical roughing pumps whenever possible If the multiplier becomes contaminated it must
196. gram system requirements vary depending on the performance required of the CIS Analyzer and on how many heads are connected and run simultaneously The CIS Analyzer can scan data at different scan speeds that effect noise floor and averaging If you choose to scan at the fastest speed and want the RGA program to keep up with the head then a faster computer I O card and graphics card might be required Procedure 1 Turn on the computer and start MS Windows 2 Insert Disk 1 of the RGA Windows software in the 1 44 Mbytes 3 5 floppy drive of the computer 3 Run Setup 4 The software is automatically and completely installed by the RGA installation program Read and follow all instructions 5 An SRS RGA program group with the RGA Program icon is automatically created at the end of the installation process 6 Take a moment at this time to read the RGA Windows Software Chapter of this manual Turning on the CIS Analyzer l Power up the CIS Head Standard CIS heads are powered up by turning on the external 24V power supply Units with a built in power module Option 02 have a power switch on the back panel of the ECU box When power is applied to the ECU a firmware routine automatically checks the external voltage level and turns on the green Power LED if the voltage is within the acceptable range of 24 2 V DC The CIS Head is now ready to communicate with the computer CIS Quadrupole Gas Analyzer Running the
197. h the change in output signal of the RGA is proportional to the corresponding change in partial pressure Linear response range The partial pressure range over which linearity in the signal response is observed See linearity Mass to charge ratio The mass to charge ratio M Q is defined as the ratio of the mass number M of the ion to its charge Q measured in units of the electron charge e For example doubly charged ions of argon isotope 36 Ar and singly charged ions of water H gt O have M Q 18 and cannot be differentiated from each other with most mass spectrometers Note Mass spectrometers do not actually measure the molecular mass directly but rather the mass to charge ratio of the ions For singly charged ions the mass to charge ratio is numerically equal to the mass of the ion in atomic mass units amu SRS Quadrupole Gas Analyzers 4 Glossary of Terms Mass analyzer Probe component The portion of the mass spectrometer probe that separates the ion beam into its various mass to charge ratio components Also referred to as Quadrupole mass filter Mass Number M The mass number M is the sum of the number of protons and neutrons in an atom or molecule Mass peak The ion current pattern in the vicinity of maximum amplitude by scanning through a small portion of the mass range containing ions of a single mass to charge ratio Very often the term mass peak refers to the signal developed from singly char
198. hannel devices reduces this problem however frequent calibration of the multiplier gain against the FC output is recommended for reliable quantitative measurements This is done automatically with the RGA Windows software Gain degradation limits the lifetime of all electron multipliers Eventually the gain drops to unacceptable values and the multiplier needs to be replaced As a rule of thumb the multiplier should be replaced when the required gains can no longer be achieved by increasing the bias voltage The lifetime of electron multipliers is ultimately dependent upon the accumulated charge drawn from the multiplier Gain degradation typically starts at accumulated output current values of a few thousand nAmp hr However the lifetime also depends critically on the gas environment and the duration of transient signals Contamination by organic compounds i e diffusion or mechanical pump oil and the interaction with highly reactive gases must be avoided at all times It has been found that in many cases channel multipliers may be successfully refreshed CIS Quadrupole Gas Analyzer Pumping System Requirements 3 19 by cleaning them in high purity isopropyl alcohol The procedure is described in the Maintenance chapter CDEM Refreshment section and even though it is not guaranteed to always work it is worth trying as a last resort before discarding a multiplier Channel electron multipliers have a history of high performance and de
199. hat are attainable with the CIS Analyzer CE Cover Tee CIS Noute Fangs Side Port for Turbo Pura p techn ent Figure 3 Cross section of the SRS CIS 1 Repeller 2 Filament 3 Ionization Tube Anode 4 Alumina insulator and seal 5 Spring washer 6 Emission Slit 7 Alumina insulator and seal 8 Extraction plate 9 Exit aperture The CIS was designed to fit the same quadrupole mass filter that is standard in the SRS RGA analyzers SRS models RGA100 RGA200 and RGA300 while keeping in mind the same basic requirements of simplicity cleanliness and ease of maintenance CIS Quadrupole Gas Analyzer 3 4 lonizer The calculated gas conductances of the standard CIS apertures assuming room temperature Ar gas in molecular flow regime are 0 3 Ls for the electron slit and 0 2 Ls for the ion exit hole The tube itself is approximately 1 long and has an internal diameter of 0 27 corresponding to a conductance of 1 5 Ls The effective conductance calculated at the tube s entrance i e considering the length of tube and the two holes in series is approximately 0 4 L s The pressure in the ionizing region is very uniform and virtually identical to the process pressure The conductance numbers for the CIS are very similar to those in most commercially available CIS systems and correspond to a high conductance between the process chamber and the analyzer A high conductance is desirable to minimize backstreaming from the
200. he OIS is exposed to the same vacuum environment as the rest of the sensor makes the ionizer sensitive to the impurities outgassed by the rest of the quadrupole assembly A serious problem for a lot of RGA users particularly in the UHV range is H20 outgassing from unbaked RGA s However lots of other species are also present that can affect the background readings For example high Ar backgrounds can be expected if the sensor was recently exposed to large levels of the gas because it tends to get adsorbed on all surfaces and desorbs slowly The ionizer is also sensitive to impurities generated at the hot filament Gas molecules can suffer thermal cracking and chemical reactions at the filament surface and the products of the reaction can easily find their way into the ionization region The impurities generated in this fashion are usually an important source of contamination of the ionizer s surfaces and have a serious effect on the RGA s long term stability For example CO and CO are emitted by most hot filaments Carbon impurities in the filament wire react with Oxygen and easily find their way into the ionizer and vacuum system Partial Pressure Reduction PPR systems 10 Torr lt P lt 10Torr RGA s are not limited to the analysis of gases at pressures below 10 Torr Higher gas pressures can be sampled with the help of a differentially pumped pressure reducing gas inlet system PRGIS consisting of a restriction and a vacuu
201. he QMF same as MRO command QMF Programming tips e Take advantage of the stabilization feature of the ML command whenever possible For example Do not send any new commands to the CIS Head once the QMF has been set to the specified mass value or otherwise recall the ML command whenever practical to refresh the QMF RF DC settings e A typical application of the ML command involves monitoring a single mass concentration looking directly at the linear output of the CDEM anode with a boxcar or transient digitizer All SRS mass spectrometers can be configured at the factory to provide direct access to the analog output current of the electron multiplier Ask SRS or your local representative about the Option03 hardware enhancement e Use the MLO command to turn off the RF DC bias when finished performing measurements and before quitting the program controlling the instrument e Itis good practice to perform an analog scan before using the ML command to assure the correct tuning i e correct peak locations and widths of the quadrupole mass filter Perform a complete Peak Tuning Procedure as described in the Tuning chapter of this manual if shifts in the peak locations are observed Error Checking the CIS Analyzer Several firmware driven checks automatically test the CIS Head when the unit is turned on and continuously monitor the internal workings of the instrument A Background Filament Protection Mode is activated when the filament is t
202. he RF DC ratio determines the filter selectivity Ions that successfully pass through the filter are focused towards the detector and the resulting analog current is measured by the very sensitive electrometer A brief note on Mass Units in Mass Spectrometry Since molecules are so small it is convenient to define a special type of mass units to express the masses of individual ions The atomic mass unit amu defined as 1 12 of the mass of a single carbon atom isotope 12 i e C is the unit of molecular mass most commonly used in mass spectrometry 1 amu 1 660 540 x 107 kg To a very accurate approximation the mass of a molecule in atomic mass units amu is equal to its mass number M defined as the sum of the number of protons and neutrons in the molecule Mass spectrometers do not actually measure the molecular mass directly but rather the mass to charge ratio of the ions The mass to charge ratio M Q is defined as the ratio of the mass number M of the ion to its charge Q measured in units of the electron charge e For example doubly charged ions of argon isotope 36 CA and singly charged ions of water H5 O have M Q 18 and cannot be differentiated from each other with most mass spectrometers For singly charged ions the mass to charge ratio is numerically equal to the mass of the ion in atomic mass units amu Mass spectrometer users often use the term mass of an ion when they really mean the mass to charge ra
203. he SRS RGA software allows the composition of the vacuum system to be analyzed by two methods The most common is to measure the mass spectrum of the vacuum This provides a fingerprint of the residual gases in the vacuum system A second method is to track specific species or peaks of the mass spectrum The first method analog scan mode is most useful when the user does not know what is present in the chamber Once the identities of the species have been determined individual peaks can be tracked using either pressure vs time table or annunciator mode The Mass Spectrum diag TE dome t The fundamental operation of the RGA is as a mass spectrometer Figure 1 shows a graph of partial pressure versus mass which was measured with an RGA with an electron multiplier detector Figure 1 Partial Pressure vs Mass The scan was taken of a vacuum system near its ultimate vacuum The pressure axis is plotted on a logarithmic scale so that a large range can be seen The log scale makes the peaks appear wider than when plotted on a linear scale This scan from 1 to 75 amu shows some gases commonly present in vacuum chambers There are many peaks but they are caused mainly by 7 species Hydrogen is at 2 and helium at 4 Water gives primary peaks at 16 17 and 18 due to the species O HOT and HOT The smaller peaks at 19 and 20 are due to O which is naturally present at 0 2 Nitrogen is at 28 and also causes the peaks at 14 by atomic N and t
204. he bottom PCB so as to reduce the effects of noise and ground offsets between the PCBs The CPU may scan the mass filter by ramping the 18 bit DAC output between 8 56mV for 1 amu and 2 56V for 300 amu Foldback Current Limiting The RF output is approximately linear in the RF primary drive current The scale factors for the detected RE SET and the measured RF primary drive current RF PRI 1 5V A were chosen so that RE SET should always be larger than RF PRI if the system is operating properly In the case of a failure which causes excessive primary drive current the output of the difference amplifier U304B goes positive as RF PRI goes above RF SET The output of U304 will limit the primary drive current as the current through D304 increases In this case which is detected by the CPU as RF_PRI gt RF_SET the RF level will be less than the level set by the 18 bit DAC CIS Quadrupole Gas Analyzer Description of Schematics 9 11 The 18 bit DAC output is also used to set the DC potentials applied to the mass filter RF SET is multiplied by 4 by the differential amplifier U304A which uses the bottom PCB for its ground reference The output of U304A is passed to the bottom PCB via JP301 to control the DC bias sources Schematic name QMSE B1 Mass filter RF Supply The Toroid The design approach was dominated by the characteristics of the RF transformer This iron powder toroid provides a step up of 39 1 for the RF The secondaries h
205. he doubly ionized N Molecular oxygen shows a peak at 32 and an isotope peak at 34 Argon shows a peak at 40 SRS Residual Gas Analyzer 4 Appendix A Carbon dioxide shows a peak at 44 and a peaks for CO and C at 22 and 12 The other peaks are caused by fragments of these species and contaminants The presence of air components in the spectra might lead us to believe that the system is leaking but this is untrue The hybrid turbomolecular pump has simply reached its compression limit The foreline of the pump was operating at a total pressure of 0 5 Torr thereby the compression ratio is in the 10 range as the pump specifications indicate Nitrogen oxygen and argon are all present in the same ratios as standard atmosphere The presence of helium is interesting because it is present in the atmosphere at about 7 ppm Its peak might be expected 6 decades smaller than the nitrogen peak The low compression ratio of the turbo pump for helium 10 explains why the peak is only three decades smaller The ability to detect these common species and many others is the essence of the RGA The fragmentation of molecules in the ionizer of the RGA gives each molecule a distinct fingerprint The fragmentation patterns for many molecules is available from the library in the SRS RGA program Keeping a historical record of the typical spectrum of a vacuum system allows the appearance of peaks to be instantly detected For instance the peak at 48 in
206. he quadrupole rods should be approximately two decades lower than the chamber pressure i e 1 2 10 Torr Consult SRS or your authorized representative if large deviations in this pressure reduction factor are observed Important e Ifa shut off valve is connected between the CIS Ionizer and the gas chamber and an extra total pressure gauge is part of the pumping system the following procedure can be followed to leak test the vacuum connections close the shut off valve and use the output of the extra gauge to leak test the vacuum seals The CIS probe is pre cleaned and leak tested at the factory The system should pump down very quickly with an ultimate pressure only limited by the outgassing rate i e mostly water from the internal walls of the CIS Probe Check the vacuum seals if a leak in the vacuum system is detected or suspected after the vacuum components are installed e Contact SRS immediately if a leak in the feedthru flange is detected or suspected e A thorough bakeout of the CIS Probe is recommended before the CIS is used for actual measurements Consult the Probe Bakeout instructions in the Maintenance chapter of this manual for details e An overnight pump down is needed in instruments with the electron multiplier option Option 01 Consult the CDEM Preconditioning section in the Maintenance chapter of this manual before applying any voltage across the CDEM Electronics Control Unit Installation The Electronics Control U
207. he two knobs to lock the ECU box in place at the end of the ECU installation procedure Do not overtighten the knobs Hand tighten only Power entry module Option 02 Use this connector to power the CIS Head directly from an AC outlet Use the three wire power cord provided by SRS to connect the instrument directly to a properly grounded AC outlet Use the built in switch to turn the unit on off Refer to the first page of this manual for instructions on selecting the correct line voltage and fuse The built in power module Option 02 has universal input 90 264 VAC 47 63 Hz and completely eliminates the need for an external 24VDC power supply connection CIS Quadrupole Gas Analyzer Rear Panel 4 7 LED Functionality LED s on the rear panel of the ECU provide constant feedback on the status of the filament electron multiplier electronics system probe and communications and alert the user of any detected errors This section describes in detail the function of each LED Figure 5 ECU LED s STATUS Green LED s Power The Power LED is turned on whenever the CIS Analyzer is successfully powered up When power is applied to the ECU a firmware routine automatically checks the external voltage level and turns on the Power LED if the voltage is within the acceptable range of 24 2 V DC The same test is performed in units with built in power modules Option 02 to check the voltage output of the internal switching power supply
208. her system clocks crosstalk from the clocks will be synchronous and will generate a fixed offset to the signal which may be measured and subtracted instead of noise The clock division for the 28 8 kBaud rate is done by the microcontroller the rest of the clock division is done by U108 a 74HC4020 14 stage ripple divider The 172 8 KHz square wave is formed into a 100 ns wide pulse to be used as a switching power supply sync pulse which is divided by two by the power supply controller U109 a 74HC74 dual D type flip flop provides the complimentary drive required for the RF and high voltage inverter circuits Either of these drives may be turned off both Q and Q outputs set high by setting the control bits RF ON or HV ON low RS232 Interface The microcontroller communicates with a host computer via the RS232 interface The RS232 interface is configured as a DCE data communications equipment at a fixed baud rate of 28 8k with hardware handshaking via CTS clear to send and RTS request to send and uses a PC compatible female DB9 connector So the quadrupole will transmit data on pin 2 receive data on pin 3 assert CTS on pin 8 and look for RTS on pin 7 Pin 5 is the signal and chassis ground Schematic name QMSE T2 IN calibration The current signal from the Faraday cup or electron multiplier is converted to a voltage by the logarithmic I V converter see schematic QMSE V1 This converter requires careful calibration and bi
209. hipped with a power cable that connects the any internal PC power plug Each relay has a Connect Normally Open and Normally Closed screw terminal connection The board has 8 mounting holes and comes with standoffs for testing on a lab bench See attached data sheets for more details I O Screw Terminal Board 12 22 AWG terminals optional This is a simple 4 x 4 screw terminal board that can connect directly to the TTL I O card cable to give easy access to the TTL signals Installation Procedure Every I O board is shipped with an installation diskette from the manufacturer Computer Boards INC Please read all the documentation and manuals that are shipped with the I O board before installing it You must use the I O board installation diskette Instacal program before attempting to use the RGA program with the board Installation Instructions 1 Make sure the RGA program and RGA Head are operating properly before installing the I O board 2 Configure the I O board hardware switches following the manufacturer s directions see the Computer Boards INC manual for your board SRS Residual Gas Analyzer Appendix C 3 3 Install the board in the computer following the manufacturer s directions see the Computer Boards INC manual for your board 4 Turn on the computer and run the Install exe program on the diskette that shipped with the board Keep in mind the following points a Select No when asked if you will be using
210. his current flows through the 698Q feedback resistor R312 in parallel with R322 which is selected to calibrate the detector s sensitivity The output of the charge pump s I V converter U305 is filtered and attenuated by the 3rd order elliptic filter C303 305 and L300 which has a characteristic impedance of 200 and a notch at 5 6MHz which corresponds to the second harmonic of the detected RF signal The potentiometer at the output of the filter P300 is adjusted to provide a voltage of Vpp 1000 This signal is used as the feedback signal to control the RF amplitude The adjustment of P300 the RF amplitude detection gain potentiometer is very important in order to maintain constant resolution and sensitivity throughout a scan P300 should be adjusted so that He and Kr have the same resolution with RES CTL at a fixed nominal level of 2 50VDC From here empirical adjustments to RES CTL vs amu may be made to optimize the instrument s performance but to first order RES CTL will be a constant Factory cal only with DS 0 RF Amplitude Control The detected RF amplitude signal VPP 1000 is compared to the RF level control RE SET from the 18 bit DAC U303 If the detected level is below the set level then the output of U306 slews upward increasing the primary drive increasing the RF level until the RF level reaches the set level U306 is configured as a differential amplifier with a gain of 5 which uses the ground reference from t
211. ifferent sensitivity factors for the same gas since they correspond to three different sets of ionizer conditions Important In order to separate the gain of the electron multiplier from the intrinsic sensitivity of the CIS head the sensitivity factors are always defined for Faraday Cup detection A separate Electron Multiplier Gain Factor is used to correct the ion signals when the electron multiplier is active See the Electron Multiplier Tuning section for details Regardless of the operating mode the partial pressure sensitivity of the CIS Analyzer to a particular gas is determined following the general steps listed below 1 Refresh the calibration of the electrometer using the Calibrate Detector command Head Menu of the RGA Windows program or the CL command of the CIS command set 2 Start with the vacuum system at base pressure preferably under 10 Torr 3 Select Faraday cup detection and choose the desired operational parameters for the instrument Note In general this involves choosing one of the three basic operating modes for the CIS Analyzer RGA CIS 35 or CIS 70 CIS Quadrupole Gas Analyzer 6 12 Sensitivity Tuning Procedure 4 Perform a few analog scans on the chamber to assure that the contributions from all other gases to your measurements can be neglected Check the quality of the analog spectra and peak tune the instrument if needed 5 Introduce the pure calibration gas into the vacuum system at a know
212. ight after the CIS Head buffer is flushed e Itis good practice to perform an analog scan before triggering a large set of histograms to assure the correct tuning i e correct peak locations and widths of the quadrupole mass spectrometer Perform a complete Peak CIS Quadrupole Gas Analyzer Scan and Measurement Commands 5 43 Tuning Procedure as described in the Tuning chapter of this manual if shifts in the peak locations are observed e The CIS Analyzer has the ability to store a complete scan in its output buffer The scan remains in memory until all the data is transmitted out to the host computer over RS232 As a result of the high acquisition rate there might be a delay between the time at which the data is collected and the time at which a complete spectrum is displayed by the host computer The time lag between data acquisition and display depends on a large number of factors including the scan rate NF setting the host computer s processing speed and the amount of handshaking activity over the RS232 lines e Before a new scan starts the CIS Head checks its internal memory to make sure that no data from any previous scan is pending to be transmitted If data is still pending the CIS Head must finish transmitting it before the new scan can start This process may result in a delay from the time the scan trigger is received to the time it actually starts Using the HS1 command and waiting until the whole scan data stream is transm
213. ikely to be encountered during measurements i e usual major components of the residual gas environment of the chamber Obviously the correct gases will be needed for sensitivity factor and fragmentation factor determinations Important Tuning should only be attempted after the unit has been warmed up with the filament on and under typical operating conditions for at least one complete hour CIS Quadrupole Gas Analyzer Tuning Options 6 3 Tuning Options The different tuning procedures including the corresponding RGA Windows commands are listed in the following table Tuning Procedure RGA Windows Cmd a Peak Tuning Peak Tuning Peak Position Peak Width Sensitivity Tuning Sensitivity Tuning Operating Modes Electron Multiplier Channel Electron Gain Tuning Multiplier adjustment a Head menu command options Consult the RGA Windows User s Manual and the RGA On line Help files included in the program disks for information on the execution of the Tuning Commands built into the program CIS Quadrupole Gas Analyzer 6 4 Peak Tuning Procedure Peak Tuning Procedure Introduction During a mass scan the peaks for the different gas species must be displayed at their correct mass to charge ratio location and their peak widths must be less or equal than 1 amu at 10 of peak height The correct location of the peaks is essential for accurate qualitative analysis and unity resolution Am 9 1 amu minimizes the overlap bet
214. ime lag between data acquisition and display depends on a large number of factors including the scan rate NF setting the host computer s processing speed and the amount of handshaking activity over the RS232 lines e Before a new scan starts the CIS Head checks its internal memory to make sure that no data from any previous scan is pending to be transmitted If data is still pending the instrument must finish transmitting it before a new scan can start This process may result in a delay from the time the scan trigger is received to the time it actually starts Using the SC1 command and waiting until the whole scan data stream is transmitted back to the host computer will minimize the problems that are associated to this feature CIS Quadrupole Gas Analyzer Scan and Measurement Commands 5 49 e Perform a complete Peak Tuning procedure on the CIS Head if the peaks in the spectrum do not appear at their correct mass values See Peak Tuning section in the Tuning chapter for procedures CIS Quadrupole Gas Analyzer 5 50 Parameter Storage Commands Parameter Storage Commands MGparam param 0 0000 2000 0000 Description Electron Multiplier Gain Storage Echo Query Response Store a value of electron multiplier CDEM Gain expressed in units of thousands in the non volatile memory of the CIS head The command is typically used together with the MV instruction to store calibrated sets of High Voltage and Gain for the Electro
215. ination with the CIS Analyzer Even the best trapped diffusion pumps backstream oil into their vacuum chambers and should never be operated in the absence of a cold trap or baffle They generally do not provide the base pressures required by the CIS analyzer they are bulky and can only be operated in an upright position With a few exceptions they all require water cooling and they consume large amounts of power during operation Start up times are considerably longer than in turbo pumps i e 5 to 10 minutes Their price advantage is offset by the problems mentioned above and usually disappears by the time the addition of an oil trap and maintenance costs are added to the purchase price Ion pumps and cryo pumps are alternative oil free pumping systems for the CIS analyzer However they are generally more expensive and less versatile than turbopumps Their use as primary pumps is only recommended in specialized applications i e where turbo pumps might not be adequate or as auxiliary pumps i e the pumps that do the work at night while the system is at base pressure Cryopumps which usually offer very large pumping speeds for water have been succesfully used to clean water backgrounds and enhance low level water detection limits of many commercially available closed source mass spectrometers A typical upgrade to the Pumping System includes the addition of a total pressure gauge dedicated to monitor the pressure on the quadrupole rods
216. ing parameter with the original factory setting for the RF Driver output 128 amu The factory value is retrieved from memory and used as the new parameter value to excecute the command as above RS Query Returns over RS232 the parameter value currently saved in memory RS Uses the current parameter value to recalculate the internal scan parameters used to step the RF during scans and single mass measurements This is often used to compensate against small temperature drifts in the mass scale caused by drifts in the output of the RF Driver Error checking The absence of a parameter i e RS is treated as an error in the parameter This parameter is protected by an internal calibration jumper JP100 and a Protection violation error will result if the jumper is in the Calibration Disabled mode see CE command CIS Quadrupole Gas Analyzer Error Byte Definitions 5 65 Error Byte Definitions The Error Bytes described in this section store the results of the firmware driven checks built into the CIS Head Use the Error Reporting commands to query the value of the bytes Important No errors are present as long as all bits in the Error Bytes are cleared The RGA Windows software supports all the Error Reporting commands and reports the errors detected based on their Error Codes The Troubleshooting chapter identifies the different problems based on their Error Codes and suggests possible causes and solutions Internal Ch
217. ingle analog scan from 1 to 100 amu at the default scan rate setting Note that each one of the command CIS Quadrupole Gas Analyzer Command Syntax 5 7 character strings must be strictly followed by a CR character in order to be detected by the spectrometer s command handler ID Identification Query MI Set initial scan mass to 1 amu MF100 Set final scan mass to 100 amu FL1 0 Turn on the filament to a 1 0 mA emission current NF Use default noise floor setting sets scan rate and averaging AP Query the number of scan points to be received by the computer SCT Trigger a single analog scan Programming tips Whenever possible immediately follow a command that sets a parameter value with one that queries the parameter setting in the instrument s memory For example the second command in the list above should be followed by a MI and a number 1 should be echoed by the CIS Head Whenever practical check for errors at the end of command execution to make sure everything went well Even though the CIS head can store multiple commands in its receive buffer it is highly recommended that the host computer wait for the response of a query before a new command especially a new query is transmitted to the CIS Analyzer This simplifies the communications and also eliminates buffer overwrites Commands that involve hardware control such as turning the filament or the CDEM on trigger diagnostic checks on the hardware as
218. inusoidal RF voltage is superimposed The other rod pair Y Z plane is connected to a negative DC voltage upon which a sinusoidal RF voltage is superimposed 180 degrees out of phase with the RF voltage of the first set of rods The potentials are represented by the expression Vyyz U Vis cos Ot where U is the magnitude of the DC voltage applied to either pair of rods Vois the amplitude of the RF voltage applied to either set of rods and is the angular frequency 27f of the RF Light ions low mass to charge ratio are able to follow the alternating component of the field For the X direction those ions will stay in phase with the RF drive gain energy from the field and oscillate with increasingly large amplitudes until they encounter one of the rods and are discharged Therefore the X direction is a high pass mass filter Only high masses will be transmitted to the other end of the quadrupole without striking the X electrodes On the other hand in the Y direction heavy ions will be unstable because of the defocusing effect of the DC component but some lighter ions will be stabilized by the alternating component if its magnitude and amplitude are such as to correct the trajectory whenever its amplitude tends to increase Thus the Y direction is a low pass mass filter Only low masses will be transmitted to the other end of the quadrupole without striking the Y electrodes The two directions together give a mass filter suita
219. ion molecular fragmentation and changes in the isotopic composition of the molecule are responsible for the effect All ions formed contribute to the mass spectrum of the molecule and define its fragmentation pattern The identification and interpretation of mass spectra must begin with a knowledge and understanding of the standard fragment patterns of atoms and molecules that may exist in the system The standard fragment patterns of most molecules commonly encountered in residual gas analysis are well established and listed in the general Partial Pressure Analysis Literature A very complete library can also be accessed through the Library Search Utility of the RGA Windows software The Gas Library has a standard text file format and can easily be read extended or modified by the user to fit his individual needs Partial Pressure Gas Analysis Tip Virtually every vacuum system will have detectable amounts of hydrogen 2 amu water 18 amu carbon monoxide 28 amu and carbon dioxide 44 amu Become familiar with these species and their fragmentation patterns and use their peaks to verify the correct performance of the instrument i e mass scale calibration and mass resolution while operating the CIS Analyzer Partial Pressure Measurement Once the different components of a mixture have been identified it is possible to use the CIS Analyzer to obtain quantitative values for the various partial pressures This section describes the basic steps
220. ion in CIS Quadrupole Gas Analyzer The SRS Closed lon Source Quadrupole Gas Analyzer 2 3 the Quadrupole Probe chapter of this manual for more information on this subject Process pressures as large as 10 Torr can be monitored by adding an extra step of pressure reduction between the process chamber and the CIS and without the need for any extra pumps Consult the High Pressure Sampling section in this chapter for more information on this subject The ECU is a densely packed box of electronics 3 x 4 x 9 that mounts directly on the probe s feedthru flange and connects to a host computer It contains all the electronics necessary to operate the instrument It is described in detail in the Electronics Control Unit chapter of this manual It includes several regulated power supplies a microprocessor control firmware and a standard RS232 communications port It is powered by either an external 24 VDC 892 5 Amps power supply or an optional built in power module Option 02 which plugs directly into an AC outlet A unique temperature compensated logarithmic picoammeter built into its box measures the ion currents collected by the Faraday cup FC or electron multiplier CDEM The electrometer is completely autoranging and measures both positive and negative currents with the same accuracy and resolution Its operating range covers current magnitudes between 10 and 107 A providing six orders of magnitude dynamic range during single
221. ions but the spectra reveals that the system is heavily contaminated with oil This could have been caused by improper valve sequencing or a saturated oil trap Without an RGA only operating procedures for valves and a maintenance schedule for traps can ensure that the cleanliness of a vacuum system is maintained With the RGA the cleanliness can be guaranteed before a process or experiment begins Solvent Contamination Oil contamination is common in vacuum systems Cleaning parts with solvents is a common approach to removing this contamination We have observed that organic solvents such as acetone and 1 1 1 trichloroethane TCE are more tenacious contaminants than the oil they are designed to remove Figure 3 shows the spectrum of a vacuum system contaminated with TCE as evidenced by the major peaks at 97 and 99 and the minor peaks at 61 63 117 and 119 The paired peaks are caused by the natural isotopic occurrence of Cl and CI 75 and 25 This spectrum was measured one week after the initial contact with the solvent The TCE permeated into the o rings in the system during a cleaning step The TCE continued to outgas from the o rings for two weeks and showed no signs of stopping At that time they were removed and baked in an oven which eventually removed the TCE Torr TEE Conta manated Systm 1 D YH F 2B BP FF HH F BB A BS HH UG 40 Km o die ta amu Figure 3 TCE Contaminated System Data like this is invaluable to the developm
222. irectly into the CIS Head making the instrument s calibration independent from the host computer that controls it Important RGA Windows reserves the use of the first three members of the table XA1 2 and 3 for the storage of sensitivity factors for the three Basic Operating Modes of the CIS Analyzer RGA CIS 70 and CIS 35 modes Do not modify those memory locations if you plan to use RGA Windows to control the CIS Analyzer The three sensitivity factors are measured at the factory for N2 28 amu and stored in units of 10 A Torr before the unit is shipped out Please consult the General Operation Chapter of this manual for details on the Basic Operating Modes of the CIS Analyzer Important The numeric values stored in the Parameter Storage Table are not used internally by the CIS Head in any way during operation They can only be used by the software programs that operate the CIS Head from the host computer CIS Quadrupole Gas Analyzer 5 52 Parameter Storage Commands Parameters XAQ Clear the pointer so that XV does not access any member of the Parameter Storage Table XAO followed by XV returns a zero XAparam param 1 10 Point to a specific member of the Parameter Storage table so that XV can get to it For example XA4 followed by XV returns the value of the fourth member of the Parameter Storage Table XA Query the pointer value Use to verify which member of the table XV will interact with Error checking
223. is and execution of a command including the specific ways in which they are reported Command errors Bad Command Name The first two characters in a command string must be letters case insensitive and must be part of the CIS Command Set otherwise the Error LED is flashed Bit 0 of RS232 ERR and Bit 0 of STATUS are set and no command is executed Command too long error 14 characters are received over RS232 without a CR ever being detected The Receive buffer is flushed Bit 2 of RS232 ERR and Bit 0 of STATUS are set and no command is executed Note that the LED is not flashed for this error only exception to the rule Parameter errors Bad Parameter error Many different possibilities lead to a bad parameter error The number parameter is out of the command s acceptable range e A is not strictly followed by CR in a Query command e A is not strictly followed by CR in a Default command A non zero fractional part is found in a parameter that can only be an integer No parameter is found in a command that strictly requires one e A parameter other than a is found in a Query only command A default parameter value is used with a command that does not have one defined All Bad Parameter errors are reported flashing the Error LED and setting Bit 1 of RS232 ERR and Bit 0 of STATUS No command is executed Parameter conflict error When the parameter is in conflict with some other related para
224. it you are connected to Important e If you make a typing error the Error LED on the back plane of the ECU box will blink two or three times Press Enter and retype the command e The Backspace character is not processed by the CIS Head e When you are done using RGA Com you must disconnect the COM port or exit the program otherwise no other Windows program can communicate with the open COM port CIS Quadrupole Gas Analyzer RS232 Interface 5 5 RS232 Interface The RS232 interface connector of the CIS Analyzer is a standard 9 pin type D female connector configured as a DCE transmit on pin 3 receive on pin 2 with full RTS CTS handshaking enabled The CTS signal pin 8 is an output indicating that the CIS Unit is ready while the RTS signal pin 7 is an input that is used by the host computer to control the instrument s data transmission The communication parameters are fixed at 28 800 baud rate 8 databits no parity 2 stop bits Cable connection Use a straight through RS232 cable with 9 pin type D connectors to connect the computer usually DTE to the ECU The DB9 to DB25 adapter provided with the unit will be needed if the computer has a 25 pin Type D connector Important If you use your own RS232 cable check the connectors to make sure all the necessary handshaking lines are connected correctly LED Indicators To assist in programming the CIS Head has two status LED s on the rear panel of the ECU b
225. itted back to the host computer will minimize the problems that are associated to this feature MFparam param 1 M MAX Description Final Mass amu of mass spectra Analog and Histogram Echo Query Response Set the Final Mass value in amu for Analog and Histogram scans The last ion current transmitted during an Analog or Histogram scan corresponds the mass to charge ratio specified by the MF parameter Important Note that the final mass setting is shared by both histogram and analog scans and must be an integer number Parameters Three possibilities MFparam param 1 M MAX The parameter represents the final scan mass in amu units The upper mass limit depends on the SRS CIS model number M MAX 100 for CIS 100 200 for CIS200 and 300 for the CIS300 units MF The final mass value is set to its default value Default value M MAX 100 for CIS100 200 for CIS200 and 300 for the CIS300 MF Query the value of final mass to be measured during scans Error checking Number parameters must be within the specified range and be integers CIS Quadrupole Gas Analyzer 5 44 Scan and Measurement Commands The mass value set by MF must always be greater than or equal to the initial mass setting of MI or else a parameter conflict communications error is generated The absence of a parameter i e MF is treated as a bad parameter error Miparam param 1 M MAX Description Initial Mass amu of mass spec
226. ive inductor T401 to cancel the charge injected via the FET gates DC Potentials In addition to the RF DC potentials of about 1 12th the RF peak to peak value is required for the two rod pairs The op amp U403A is the error amplifier which maintains the negative potential equal to a fraction of the set RF level When DC SEI goes up the output of the op amp goes up increasing the current in Q406 increasing the current in Q407 bringing down the collector of Q407 which is the output of the negative potential voltage regulator The op amp U403B is the error amplifier for the positive potential The positive potential is compared to the negative potential by R431 and R432 When the negative potential increases the non inverting input to U403B will go down lowering the op amp output increasing the current in Q405 increasing the current in Q404 thereby increasing the positive potential until it matches the magnitude of the negative potential Schematic name QMSE B2 Filament Heater Supply The sensitivity of the quadrupole depends on the filament emission current which depends on the filament temperature and bias with respect to the grid As the grid to filament bias is fixed to optimize the electron impact ionization cross section the filament emission current is controlled by controlling the filament temperature via the filament heater current s duty cycle A switching power supply which is synchronized to a sub multiple of the master
227. ive ions are CIS Quadrupole Gas Analyzer Pumping System Requirements 3 17 very efficiently attracted away from the FC and strike the cone at high velocity producing electrons by secondary electron emission The secondary electrons are subsequently accelerated down the four channels and produce more secondary electrons For each ion entering the cone of the CDEM and depending on the bias voltage applied up to 10 electrons come out at the back end and are picked up by a grounded plate the CDEM anode The resulting electron current is proportional to the ion current and is measured by the same logarithmic electrometer used in the FC measurements The sign of the electron multiplier currents is reversed before the current value is sent out over RS232 so that the computer does not need to do any sign flipping on the currents received when the CDEM is activated The gain of the electron multiplier is a function of the bias voltage and is measured relative to the FC signal The following figure shows a typical gain characteristic i e gain vs bias voltage curve obtained for HOT ions at 18 amu 1E8 3 Gain 1000 f 35 hehehe ech eebe 100 Mp pm pem emmpeR ppm 10 aena pm ppm ppm emp 1 i i i 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 HV Bias V Figure 8 Typical CDEM Gain Characteristic Curve Very high gain values can b
228. ix A Single Mass Measurement For vacuum systems that only need to be clean the mass spectrum is the most useful measurement During experiments and processes the partial pressure of certain species is of more interest The RGA software provides three modes that are used to measure selected peaks The selection of which mass is associated with which species is usually straightforward i e the mass of the molecule is chosen When two species have overlapping peak patterns the user chooses the strongest peak that does not interfere For example N and CO both have a mass of 28 In a system with a large CO interference N could be measured at mass 14 Because the peak at 14 is smaller than the major peak a scaling factor is required The set of peaks of interest are entered into the RGA software by the user During measurements the RGA measures only each peak Because the whole spectrum is not measured data is acquired much faster The two examples that follow show an interesting pressure vs time experiment and a method of increasing the dynamic range of measurements Pressure vs time Figure 4 shows the use of the P vs t Mode to monitor an air lock sequence The process is to open an air lock place the sample in it and move the sample into the main vacuum chamber The air lock is pumped from atmospheric to rough vacuum using the same mechanical pump as the main vacuum chamber This requires isolating the foreline of the turbo pump during th
229. l Comman0ds 1e eceee esee eee innuens seen nna nna nana suas suas anam anas asa saa a sm sn Dana 5 34 em 5 34 erem 5 35 HV param param 0 2490 7 sse eieiei ae 5 36 lj AG eater ee rer ei OE mM MM PE 5 38 NEpatam param Q Ty E eege dee 5 38 Scan and Measurement Comman0ds cl eeeee eese eiii EEERER NEEN nasa nasa sa sa aa anam ana sas Nk 5 40 PAP EE 5 40 jou T E LIRE 5 40 HSparam param 0 255 iaces ee x Rep ER pee Ree Ree Ete ehe 5 41 ME param parami L M MAX Eo 2s costs eite erbe eee ee EP eee eene ea 5 43 MIpara m param 1 M MAX E Teritorii niiin rene eade ise de ee eee ge ie eee ERR e 5 44 MRBparam param 0 M MAX eeiieeteseeciiebterte aaae ta te dae NEE KEENT 5 44 sAparam par m 10 25 ETH 5 46 SC param param 0525 e 5 47 Parameter Storage Commands eeeeeeeiieeeeeeeeeeeeeennn snnm nnn tnnnan than sna si sinas n tnn nna 5 50 MGparam param 0 0000 2000 0000 1 5 50 MV param param UE EE 5 50 XAparam param O IO I iiie e d etse ete eH de Ha Lors HB KR HE PIER HEEL unge 5 51 XVparam param 0 0000 4 99999 0999 7 isses nennen eene nennen nennen 5 52 Mass Filter Control Commands 11 e eeee eiie er eeeeee seen anna ne nena sa uasa anna sm anas asa saa a ssa Dana 5 54 MLparam param 0 0000 M MAX siiri sin ir Ei EA EEEE S EESE e ai 5 54 Error Reporting Command sccccccccesccecseseeseeeenseeeee
230. l see later the more compact design of closed ion sources makes it very natural for them to operate with 35 eV electrons without sacrificing the filaments lifetime The Closed lon Source CIS 10 Torr lt P lt 10 Torr In applications requiring the measurement of pressures between 10 and 10 Torr the problem of background and process gas interferences to the mass spectra can be significantly reduced by replacing the traditional OIS PPR configuration described above with a closed ion source CIS sampling system A cross section of a generic CIS setup is shown in the following figure Uose lon Source ES CE CEC T hounding Here Selen Si LAieclnpole hass Filter P 107 Torr Figure 3 Cross section of a generic closed ion source CIS 1 Insulator and seal 2 Ionization Tube Anode 3 Filament 4 Exit Plate The CIS Ionizer sits on top of the quadrupole mass filter replacing the more traditional OIS used in conventional RGA s It consists of a short gas tight tube with two very small openings for the entrance of electrons and the exit of ions Electrons enter the ionizing region through an entrance slit of small dimensions The ions are formed close to and attracted by a single extraction plate and exit the ionizer through a circular aperture of small diameter Alumina rings seal the tube from the rest of the quadrupole mass assembly and provide electrical insulation for the biased electrodes Ions are produced
231. lament on with an emission current setting of 0 5 mA It is a typical example of the set of commands sent to the CIS Head while programming the ionizer into the RGA Mode of operation EE70 Electron Energy 70 eV Echoes the STATUS Byte IEi Ion Energy high 8e V Echoes the STATUS Byte VF50 Extraction Voltage 50V Echoes the STATUS Byte FLO 5 Filament emission 0 5 mA and turn filament on Echoes the STATUS Byte lonizer Programming Tips e It is possible to trigger scans and single mass measurements while the filament is not turned on e Make sure the pressure is under 10 Torr before turning the filament on specially if the filament wire is made out of W e The filament is tested frequently by the microprocessor while it is emitting electrons Consult the Filament Leak and Burnt LED s after activation for immediate status feedback e Wait for the STATUS byte to be returned between commands and check it every time for possible errors e Incases were a hardware error is reported retry the command one more time before declaring a hardware problem e Default parameter settings are available for all the Ionizer Control commands CIS Quadrupole Gas Analyzer Programming the CIS Head 5 13 e Use the FLO command to turn off the filament Programming the Detector Positive ions that successfully pass through the quadrupole filter are focused towards a detector that measures the ion currents directly Faraday Cup FC or
232. lation For applications requiring the sampling of gas pressures lt 2mTorr the CIS Probe is directly attached to any standard 2 75 CF port of the vacuum chamber The CIS ionizer does not penetrate into the process chamber see Figure 1 A short wide piece of tubing establishes the connection to the process region Due to the high conductance of the ionizer the pressure in the ionization area is the same as in the vacuum chamber For systems requiring the use of Pressure Reducing Gas Inlet Systems the CIS probe is directly attached to the 2 75 CF flange of the Pressure Reducing Gas Inlet valve Warnings Use proper vacuum procedures while installing the CIS probe Set aside a clean dust free work area next to the vacuum port Wear gloves Do not talk or breathe directly into the probe s ionizer Use clean tools Do not remove the plastic plugs from the vacuum ports until the instrument is ready to be installed in the vacuum system Do not substitute parts or modify the CIS probe in any way without first consulting Stanford Research Systems or an authorized representative Failure to do this will automatically waive the manufacturer s warranty and may result in damage to the instrument and serious personal injury Protect the integrity of the Vacuum seals Do not use nonmetal seals Do not dent or scratch the knife edges of the CF flanges Verify that the vacuum port is electrically grounded before attempting the insta
233. le collisions starts to get comparable to the CIS dimensions and increasing numbers of ions get diverted and lost before they can reach the exit aperture A change in the emission current level is the main difference between the two basic operating modes of the CIS analyzer RGA and CIS Modes of operation For details on the two modes of operation consult the Basic Operating Modes section in the General Operation chapter of this manual CIS Quadrupole Gas Analyzer Quadrupole mass filter 3 9 Quadrupole mass filter Positive ions are transferred from the ionizer into the quadrupole where they are filtered according to their mass to charge ratios Ions that successfully pass through the quadrupole are focused towards the detector by an exit aperture held at ground potential Description The quadrupole mass filter is an electrodynamic quadrupole operated by a combination of DC and RF voltages It is constructed of four electrically conducting cylindrical rods accurately held in place by a set of two high purity alumina insulators CERE GE Ex Ge gt en a es c E CO yy Ne E ms Pops COO eee B d Ribbon connectors Quadrupole rods Spring loaded perforated screws Alumina spacers Figure 4 Quadrupole Mass Filter Components Round electrodes are a common replacement for hyperbolic rods in modern quadrupoles and result in reduced cost and ease of construction The stainless steel type 304 rods are 4 5 l
234. limited to a minimum value of 1 256 amu The command excecution involves two steps 1 The RF DC levels corresponding to the mass requested are calculated and set on the QMF rods based on the mass axis calibration parameter values specified by the last Peak Tuning procedure 2 The firmware stabilizes the voltage output of the RF Driver s controller against temperature fluctuations The result is very stable RF DC levels that are highly insensitive to the operating conditions of the CIS Head Important The RF DC stabilization algorithm Step 2 above remains active as long as no new commands are detected by the CIS Head Once a new command is received stabilization stops and the new command is executed Use the MLO command to turn off the RF DC bias when finished performing measurements and before quitting the program controlling the spectrometer Parameters ML0 0000 The RF DC voltages are completely turned off MLparam param 0 0040 M MAX The parameter represents the mass setting for the QMF in amu units The minimum mass increment value is 1 256 amu The upper mass limit depends on the CIS model number M MAX 100 for CIS100 200 for CIS200 and 300 for CIS300 Error checking Parameters must be numbers within the specified range The absence of a parameter i e ML generates a bad parameter error CIS Quadrupole Gas Analyzer Error Reporting Commands 5 55 Error Reporting Commands EC ED Description
235. llation of the CIS Probe on the vacuum system Hardware Requirements 1 Ifthe presence of corrosive gases in the vacuum environment is known or suspected consult SRS before installing the probe in the vacuum chamber 2 Do not operate the CIS Analyzer in the presence of strong magnetic fields Magnetic fields such as those caused by superconducting magnets or unshielded cold cathode total pressure gauges i e Penning type can affect the ion trajectories through the quadrupole filter resulting in very unreliable measurements If the presence of magnetic fields in the vacuum environment is known or suspected consult SRS before mounting the probe on the vacuum chamber CIS Quadrupole Gas Analyzer 1 6 Installation 3 The maximum operating pressure of the CIS Analyzer is 10 Torr A Pressure Reducing Gas Inlet system is required if the operating pressure of the vacuum chamber is routinely greater than 10 Torr Consult the High Pressure Sampling section in the General Operation chapter of this manual for more information on this subject 4 The probe can be mounted directly onto any standard 2 3 4 CF port of a vacuum chamber provided the following placement requirements are met The CIS ionizer must be located close to the point where partial pressures are to be measured If placed near a pump the pressure in the ionizer may be considerably lower than in the rest of the system If placed near a gas inlet or source of contamination th
236. lost to the internal walls of the ionization tube The technique of electron impact ionization requires low pressure for the efficient production of electrons and the subsequent formation of ions During normal operation the filament must be kept at pressures under 10 Torr while the ionizer is directly exposed to the process prerssures as large as 10 mTorr A careful choice of the pumping system is necessary to achieve the required pressure differentials Consult the Pumping System Requirements section in this chapter for details on this subject The ions formed within the ionization volume are extracted from the ionizer by the electric field produced by the difference in voltage bias between the anode tube and the extraction plate The extraction plate is kept at a negative potential relative to ground and its function is to draw the ions out of the ionization volume and into the filter section The repeller plate which backs the filament is biased negative relative to the filament and reduces the loss of electrons from the ion source The Repeller and the Extraction Plate are only biased while the filament is emitting electrons The technique of electron impact ionization requires low pressures for the efficient production of electrons and the subsequent formation of ions As mentioned above the CIS Ionizer can be exposed to process pressures as large as 10 mTorr without any additional pressure reduction However two problems arise in the CIS
237. lp Files for details on the tuning commands of the program The sensitivity factors are always calculated with the Faraday Cup detector A separate Electron Multiplier Gain Factor stored in the non volatile memory of the CIS Head is used by the RGA Windows program to correct the ion signals when the electron multiplier is turned on i e all data acquired while the electron multiplier is on gets divided by the gain automatically before it is displayed by the program See the Electron Multiplier Tuning section of this chapter for details CIS Quadrupole Gas Analyzer 6 14 Electron Multiplier Tuning Procedure Electron Multiplier Tuning Procedure Accurate quantitative measurements with the electron multiplier detector require the determination of the CDEM gain for all the ion peaks being measured Frequent recalibrations are recommended to correct against aging of the device The gain of the electron multiplier CDEM in the CIS Analyzer is defined relative to the Faraday Cup output which is assumed to be mass independent It can be programmed anywhere from 1 to 10 adjusting the high voltage applied across the device is highly mass dependent and changes with time due to aging The electron multiplier gain is easily calibrated since it is possible to measure the same ion current with and without the CDEM The common method of calibrating the electron multiplier gain for a given mass peak is to measure the peak intensity with the Faraday
238. m pump package Common restrictions are pinholes and capillaries which can provide pressure reductions of more than 6 decades of pressure Vacuum pump packages typically consist of a turbomolecular pump backed by a foreline pump The combined RGA gas inlet system and pumping station constitute what is usually referred to as a Partial Pressure Reduction PPR System These systems are commonplace in gas phase processes and are available from most RGA manufacturers The PPR system manufactured by Stanford Research Systems and depicted in figure 2 is a perfect example of the typical pressure reduction setup used to step process pressures down to levels acceptable to the OIS RGA The PRGIS actually contains two inlet paths to the RGA a high conductivity path for monitoring base vacuum and a low conductivity i e pressure reducing path for monitoring gases at operating pressure hi C valve a N N WOW Lj RGA sample zm valve D m g o bypass S turbo loop pump Figure 2 SRS PPR Inlet system components The high conductivity Hi C path is used when the vacuum system is at pressures below 10 Torr At high vacuum typical applications are leak testing and monitoring the ultimate vacuum of the chamber For example in a sputtering chamber the first stage of the process is always
239. make the instruments so popular The most common use of quadrupole mass spectrometers in vacuum applications is as residual gas analyzers RGA Most commercially available RGA s are very small and can be attached to virtually any vacuum chamber The prototypical RGA has an open ion source OIS and the entire analyzer operates at the pressure of the vacuum system The maximum operating pressure is 10 Torr More recently quadrupole mass spectrometers have been increasingly used as process monitors By far their most common application is for the detection of low level contaminants in process gases Modern day contamination requirements often fall in the PPM and sub PPM levels and will continue to decrease as processes become more sophisticated and the components being manufactured require additional refinement Although traditional quadrupole mass spectrometers designed for residual gas analysis have adequate dynamic range to detect PPM level contaminants in principle interferences from process gases and background interferences from the sensor itself can make the detection of PPM levels of certain contaminants difficult in practice The partial pressure detection limit of a mass spectrometer depends both upon the sensitivity of the sensor and upon the background signals that are present in its mass spectra In applications requiring the measurement of pressures between 10 and 10 Torr the problem of background contributions to the spectra ca
240. me lag between data acquisition and display depends on a large number of factors including the scan rate i e NF setting the host computer s processing speed and the amount of handshaking activity over the RS232 line As computers get faster they will be able to catch up with the CIS Quadrupole Gas Analyzer Programming the CIS Head 5 19 spectrometer s data acquisition speed and this problem will no longer need any consideration e Before a new scan starts the microprocessor checks the internal memory to make sure that no data from a previous scan is pending to be transmitted If data is still pending the spectrometer must first finish transmitting the stored data before the new scan can start This process may result in a delay from the time the scan trigger is received to the time it actually starts Using the HS1 command and waiting until the whole scan data stream is transmitted back to the host computer will minimize the problems that are associated to those delays Single Mass Measurements Single mass measurements are triggered with the MR command The parameter is the integer mass number mass to charge ratio in amu units at which the measurement is performed The type of detector and noise floor settings must be selected in advance with the NF and HV commands The precision and duration of the measurement are totally determined by the NF parameter value The scan rates and signal to noise ratios for the different NF settings
241. mei eee geseet EE EE eave veh us 5 41 HSparam param 255525 eerste e eddie ede ptem etus 5 42 MFparam param 1 M MAX SI 5 44 MlIparam param 1 M MAX 5 2 tei t C n t eR PRECES RS EAN Enk ela Ren ocn 5 45 MRparam param 0 M MAX ssssssseesseeeeeeeeeneen eene en rennen eren eren neen trennen 5 45 S Aparam param 10 225 EE 5 47 sCl param patam 0 255 9 iste ee tere ec Ere eee EE 5 48 Parameter Storage Commands eese esee eeeeeeeeen ene nna nnnn nn tn ansia sana nn nnmnnn nenn 5 51 MGparam param 0 0000 2000 0000 sess 5 51 MV param param D 249077 iine eme eere eoe ENEE 5 51 XApatram param 0 10 EE 5 52 XVparam param 0 0000 99999 9999 isses eene eene enne 5 53 Mass Filter Control Commands eeeeeeseieeseieeeeeeneeee en en nnns innt nn nn ansia nasa REENEN as 5 55 MLparam param 0 0000 M MAN nen een ene eren enne 5 55 Error Reporting Commands ieeseeeeeeeeeeeeses seen n nennen nnn nn anima natn n nin tn asas tasas nasa nananman 5 56 luem 5 56 JUD M MM M RE UE NU re 5 56 EE etitm ee derer n ete Pee era ede re RM eerte qol vedete ee XE dee eda 5 57 EMM32 caedlucititeeteii rt HR RR UH TU ire ENIM ELE RAPERE E des ao 5 57 BP Suse toc e URN e i SG and ngs Bere RR EX ERU S RUE as E 5 58 op A 5 58 in glp
242. ments to assure the correct tuning i e correct peak locations and widths of the quadrupole mass filter Perform a complete Peak Tuning Procedure as described in the Tuning chapter of this manual if shifts in the peak locations are observed e The RF DC voltages are not turned off at the end of a measurement Use the MRO command at the end of a set of measurements and before quitting a program to make sure the RF DC voltages are deactivated Storing information in the CIS Head In order to make the CIS Analyzer a stand alone mass spectrometer several Parameter Storage commands are available to store head specific information in the instrument s non volatile memory A Parameter Storage Table capable of storing up to 10 different numeric values i e elements is part of the non volatile memory of the CIS Head The command pair XA XV is used to update or query the elements of that table XA where A is for Address is used first to point at any one element within the table XV where V is for Value can then be used to query or update the value of the element previously pointed to by XA The numeric storage available through XA and XV is often used to store a variety of instrument specific calibration data directly into the CIS Head making the instrument s calibration independent from the host computer that controls it Important RGA Windows reserves the use of the first three members of the table XA1 2 and 3 for the storage of sensitivit
243. meter i e VF is treated as a bad parameter error CIS Quadrupole Gas Analyzer 5 34 Detection Control Commands Detection Control Commands CA Description Calibrate All Echo STATUS Error Byte Readjust the zero of the ion detector under the present detector settings and correct the internal scan parameters against small temperature fluctuations to assure that the correct RF voltages i e as specified by the last Peak Tuning procedure are programmed on the QMF rods as a funtion of mass In order to readjust the zero of its ion detector the CIS Analyzer measures the output of its electrometer in the absence of input ion current and under the present detector settings i e noise floor and detector type The current value obtained is stored in internal memory as an offset correction factor that is automatically used by the firmware to correct all ion currents measured i e including those from single mass measurements under the same detector settings Important e Offset correction factors for all the possible combinations of detector settings can be accumulated in the head s memory e All offset correction factors are automatically cleared after a complete recalibration CL of the electrometer is performed and also when the unit is turned off e Use the CA command every time the detector settings are changed to values that have not been used in a long time or that were not used since the unit was turned on or recalibr
244. meter value which pre existed in the CIS head the Error LED is flashed Bit 6 of RS232 ERR and Bit 0 of STATUS are set and the command is not executed Jumper Protection violation Some calibration related commands are subject to jumper protection Jumper JP100 on the digital 1 e top board of the insrument s electronics box can be used to enable disable some of the tuning features of the instrument The jumper setting is checked before the command is executed and if calibration is disabled the Error LED is CIS Quadrupole Gas Analyzer Communication Errors 5 9 flashed Bit 5 of RS232 ERR and Bit 0 of STATUS are set and the command is not executed The jumper setting provides very solid protection against inadvertently tampering with important calibration parameters stored in the instrument s memory Please refer to the CIS Command Set list to find out which calibration commands are jumper protected CIS Quadrupole Gas Analyzer 5 10 Troubleshooting Tools Troubleshooting Tools The communication interface includes a complete set of tools for troubleshooting communications between a host computer and the spectrometer s head during programming 1 Visual Clue The first clue of a communication error can be obtained watching the Error LED while communicating with the head The ERROR LED is flashed on off two times every time a communication error is detected 2 Error Queries The presence of a communication error can also be
245. minal conductance of the CIS Ionizer is 0 4 L sl For example a 10 mTorr gas can be sampled into the CIS Ionizer through an aperture with a maximum conductance of 0 04Ls 2 0 4 Ls 10 which provides a minimum 10 fold reduction in pressure General information on the design and basic operation of differentially pumped vacuum systems can be found in most vacuum technology textbooks A particular good treatment of the subject can be found in the book by John H Moore et al Building Scientific Apparatus Addison Wesley Publishing Co Redwood City CA 1989 ISBN 0 201 13187 0 Information on Pumping System Requirements for the CIS Analyzer can be found in the Quadrupole Probe Chapter of this manual General information on the use of quadrupole mass spectrometers to sample high pressure gases can be found in Appendix B CIS Quadrupole Gas Analyzer 2 12 Partial Pressure Analysis Basics Partial Pressure Analysis Basics The CIS Analyzer can perform both qualitative and quantitative analysis of the gases in a vacuum chamber Obtaining spectra with the CIS Analyzer is very simple Interpreting the spectra that is understanding what the spectra is trying to tell you about your process requires some work The following sections will introduce some basic concepts of Spectral Analysis emphasizing the main aspects of Partial Pressure Gas Analysis No assumptions are made as to the objective of the partial pressure analysis The CIS Analyzer is
246. ming the noise floor imposed by the I V converter an electron multiplier may be used The electron multiplier needs to be biased with as much as 2500VDC to provide gains as large as 10 CIS Quadrupole Gas Analyzer Circuit Description 9 5 Circuit Boards There are two main PCBs inside the ECU package The top PCB has the CPU RS232 digital ports the analog electronics for A Ds and D As and the RF amplitude detection circuit A small vertical PCB which holds the log I V converter connects to the top PCB A second small vertical PCB holds the electron multiplier s HV supply A third small vertical PCB is used to pass signals and power between the two main PCBs The bottom PCB holds all of the power electronics for the RF filament heater ionizer bias and system power supplies Four PCB s between the two main boards are used l 2 To connect to the probe For the I V converter To pass signals between the main boards To supply High Voltage to the CDEM CIS Quadrupole Gas Analyzer 9 6 Description of Schematics Description of Schematics Schematic name QMSE T1 PAO PA1 PA2 PA3 PA4 PAS PA6 PA7 PB PC 0 7 PDO PD1 PD2 PD3 PD4 PD5 PEO PEI PE2 PE3 PE4 PES PE6 PE7 CIS Quadrupole Gas Analyzer Microprocessor An MC68HC11E9 microcontroller is used to control the system and to communicate with the host computer This central processing unit CPU also has RAM ROM EEPROM UART o
247. mmands are commonly used to test the quality of the RS232 interface to reset the communication buffers to scan the hardware for problems and to reset the instrument to its default factory preferred parameter settings Initializing the CIS communications The two commands most often used after connecting to the head are ID Identification Query Echoes the ID string INO Clear communication buffers Echoes the STATUS Byte The ID command is used to test the RS232 interface The ID String stored in the CIS Head is returned to the computer and the integrity of the RS232 link is assured once the character string is received The ID string also contains useful information such as model and serial number of the CIS head The INO command clears the RS232 buffers runs a fresh set of tests on the ECU s hardware and sends back the STATUS Byte Check the value of the STATUS byte for potential errors Programming tips e Use the INO command every time there seems to be problems with the RS232 communications The following procedure is recommended in those cases Reset the buffers in the computer Send a few carriage returns to clear the receive buffer Send the INO command to reinitialize the instrument s buffers Wait for the STATUS error byte to come back Test STATUS for possible errors nue Lr E This trick is very useful to reset communications on both ends and is often implemented as a menu item e The ID command is used fo
248. n Several different signals and a ground reference may be multiplexed to a 16 bit A D converter by U201 a 74HC4051 The control bits MPX 0 2 are used to select one of the CIS Quadrupole Gas Analyzer Description of Schematics 9 9 8 inputs The selected input is amplified by U202A by 2x to scale the input for the 10V range of the A D converter U203 The CPU can measure the offset of the input multiplexer op amp and A D converter by selecting input X7 the circuit ground The measured offset is subtracted from readings taken for the other inputs A conversion is initiated by CS ADC16 going low while R C is low CS_ADC16 is asserted when the 675 Hz convert clock from the 74HC4020 U108 goes low provided that CS VETO MISC port bit 7 is low The 675 Hz convert clock going low also initiates an IRQ to the CPU In response to the IRQ the CPU sets CS VETO high which sets CS ADC16 high and sets R C high to allow the data to be read The BUSY output will remain low for up to 20us during a conversion When BUSY goes high the CPU returns CS VETO low which again asserts the CS ADCI6 this time with R C high and reads the data from the ADC via the SPI Since the ADC shifts its data on the rising edge of the data clock i e data should be read on the falling edge of the data clock the inverted SPI clock is used as the data clock to the ADC This will also permit simultaneous transmission of data to the 18 bit RF amplitude control D
249. n Multiplier Important The gain is not used internally by the CIS Analyzer to correct the ion currents measured with the Electron Multiplier it is simply stored so it can be read and used by any host computer connected to the instrument For example RGA Windows automatically divides the ion current readings obtained with the CDEM detector by the gain value value returned by MG As expected this command is only available in heads with a CDEM option Option 01 installed See MO command for details Parameters MGparam param 0 0000 2000 0000 The parameter representing the CDEM gain in units of thousands is stored in the non volatile memory of the head MG Electron Multiplier Gain parameter query Error checking The absence of a parameter i e MG is treated as an error No default value is available A bad command communications error is reported when this command is invoked in a unit with no CDEM option installed See MO command MVparam param 0 2490 Description Electron Multiplier Bias Voltage Storage Echo Query Response Store a value of Electron Multiplier CDEM Bias Voltage in units of Volts in the non volatile memory of the CIS head The command is typically used together with the MG instruction to store calibrated sets of Bias Voltage and Gain for the Electron Multiplier Important The voltage value is not used internally by the CIS Head to set the bias voltage of the Electron Multiplier it
250. n be significantly reduced by replacing the RGA with a closed ion source CIS sampling system The following sections of this document describe the performance specifications of open and closed ion source quadrupole mass spectrometers The main objective of this information is to introduce the basic concepts required to choose the best gas analyzer for any practical application and to discuss some of the basic operating principles that must be kept in mind to assure the optimum performance of the instrument selected Residual Gas Analyzers P lt 10 Torr The prototypical RGA has an open ion source OIS and is attached directly to the vacuum chamber so that the entire analyzer is at the same pressure as the rest of the vacuum system The maximum operating pressure is 10 Torr In high vacuum applications such as research chambers surface science setups accelerators aerospace chambers scanning microscopes outgassing chambers etc RGA s are effectively used to monitor the quality of the vacuum and can easily detect even the most minute impurities in the low pressure gas environment Trace impurities can be measured down to 10 TT Torr levels and sub PPM detectability is possible in the absence of background interferences During system troubleshooting RGA s are also used as sensitive in situ helium leak detectors In the semiconductor industry RGA s are best used in evaporators sputterers etchers or any other high vacuum system
251. n of the mass filter Newly formed ions are attracted by the negative potential of the extraction plate and passed to the ion filter where they are decelerated by the ground potential at the central axis of the quadrupole rod assembly Hence the anode voltage defines the kinetic energy of the ions as they enter the ion filter Ion energy determines the time spent by the ions in the filter and hence limits the resolution that can be obtained It is well established that the resolution limit is governed by the number of cycles of RF field to which the ions are exposed before they reach the detector In practice the minimum resolution Am oz is mass independent linearly related to the ion energy and inversely proportional to the square of the product of the quadrupole length and frequency The two available ion energy settings correspond to ultimate resolutions of approximately 0 2 and 0 3 amu well under the 1 amu factory default setting Ion energy also determines the time spent by the ions in the fringing fields at the entrance and exit points of the filter Ions passing through the fringing fields can collect high transverse velocities and are more likely to collide with the quadrupole rods and never be collected at the detector As a result ion signals i e sensitivity generally increase with ion energy The extraction plate negative potential can be adjusted to any value within the range of 0 to 150 V In general the voltage is selected so as
252. n or calculable pressure Recommended pressures are 10 Torr for the RGA Mode and 10 Torr for the CIS Modes 6 Runa few analog or histogram scans on the sample gas to assure the purity of the calibration gas 7 Measure the ion current signal for the principal mass peak of the calibration gas i e usually the parent molecule peak using the Faraday cup detector Extract the peak value from spectral scans or measure it directly using the single mass measurement mode of the CIS Analyzer 8 The ratio of this ion current signal to the pressure of the gas is the partial pressure sensitivity factor for the present mode of operation 9 The sensitivity factor in units of microA Torr can be saved into the non volatile memory of the CIS Head using the XA XV command pair An individual sensitivity factor can be saved for each one of the three modes of operation of the CIS Analyzer The parameter value saved is automatically used by RGA Windows as a conversion factor between the ion currents received from the head and the partial pressure units selected by the user See the CIS Command Set listing for details on the XA and XV commands Important The sensitivity factors calculated in this fashion are highly dependent on the ionizer s operating conditions Change the instrument parameter settings to those of your measurements prior to the calibration if necessary Note The underlying assumption when using sensitivity factors in quantitative cal
253. n through the capillary and directly to the diaphragm pump i e bypasses the RGA The pressure at the exit of the capillary is about 1 mbar A small amount of the sampled gas is diverted to the RGA through an aperture This configuration improves the response time by two methods First the pressure on the high side of the aperture is held to about 1 mbar But even this pressure would give a time constant of 3 5 seconds in the 1 2 inch dead volume example mentioned above The second method to decrease the time constant is to ensure that any dead volume is well mixed After the capillary the gas is traveling at significant velocity several meters per second Proper layout of the inlet tubing will use the kinetic energy of the sampled gas to mix the dead volume in a sense keeping the volume alive Figure 5 shows the response to bursts of gas at the inlet of an atmospheric sampler designed with the above considerations The sub second response and cleanup are almost as fast as the RGA can acquire data SRS Residual Gas Analyzer 6 Appendix B 1000 m ber D 1 5 mber het Capillary Apereture Drs22 AE Hybrid Turbo Pump GA Bypass Valve Disphragn Pump E Figure 4 High Pressure Sampling Using Bypass Pumping LOT 4 07 SOT pressure 207 D 1 z 3 ime Gi Figure 5 Response of Bypass Pumped System to Gas Bursts Glass capillaries are available with small enough bores to reduce pressure from 1000 mbar to 1
254. nalyzer is usually operated at unit mass resolution throughout its available mass range the parameter value can also be interpreted as the approximate number of ion currents to be collected for each mass peak in the spectrum Parameters SAparam param 10 25 The parameter specifies the number of steps per amu collected during analog scans SA The number of points per amu value is set to its default value Default 10 CIS Quadrupole Gas Analyzer Scan and Measurement Commands 5 47 SA Query Returns the SA parameter value currently in use by the analog scans Error checking Number parameters must be integers and within the specified range The absence of a parameter i e SA is treated as an error SC param param 0 255 Description Analog Scan Trigger Echo Ion Currents Excecute one or multiple analog scans under the present scan conditions The scan parameter can be set for single multiple and continuous scanning operation Analog scanning is the most basic data acquisition mode of the CIS Analyzer During analog scanning the quadrupole mass spectrometer is stepped at fixed mass increments through a pre specified mass range The ion current is measured after each mass increment step and transmitted to the host computer over RS232 The mass range for the scan is set in advance with the commands MI Initial Mass and MF Final Mass and the mass increments are fixed with the command SA Scan rate and detecti
255. nce This chapter describes how to maintain the components of the quadrupole probe The ECU does not have any serviceable parts and should not require any routine maintenance In This Chapter Warnings E 7 3 Probe BakeoUt eene E E EENE ASA E a EAA RE AA T 7 5 toen 7 6 l iz r Replacement meo 7 7 On eer ES 7 7 toen 7 7 Filament Replacement ccccssecceceseeeceeesneeeeeeseeeeeeesneeseeesneeseeesneeseeesneesesssneeseeesneeseessneeseessneeseeseneesesssnes 7 10 Handling and care of the filaMent ceeeeccseeeeeeeeseeeeeenseeeeeenseeeeeenseeeeeenseneeeenseeeeeeeseenenenseenenes 7 10 Equipment setts ease ee ce ea redo ee ce ee eee le eect oe ei es ede een tet 7 10 Procedure morirs oS SoS SS Sn ere 7 10 CDEM Handling and Care ssecccsecesseeeeseeeeeseeeeeeesesneeensneeenseeesaaesaseeeeaseaessaesasaaesaaneeeneeeessaesaseaeensnaeeenes 7 13 Handling and mounting ee eeeeeeeeeeeeee eee nennen nenne nnne nennt nnn nn nnmnnn nnmnnn nnmnnn nnne sn nn nnns 7 13 ruote 7 13 Operating temperature ueeeesieeseieeeeeseeeees seen nnn nn enhn tn nns na natnm asa tn Rash snas snas anna natn nasa a 7 13 Bakeout temperature eeeeeeee eiie eee nennen nannte nannten nasi nenna nnmnnn nnmnnn nnmnnn nenna 7 13 Operating volkage ee cesceetactee EE
256. nds get enabled 4 Turn on the filament e Click on the toolbar s Filament button K l e The ionizer is biased with default voltage values and the filament is turned on to the default emission current It takes a few seconds for the filament wire to warm up during which a small informative dialog box is active The Filament button remains highlighted as long as the filament is emitting electrons CIS Quadrupole Gas Analyzer 1 14 Running the CIS Quadrupole Gas Analyzer e The filament emission can be toggled on off at any time clicking on the Filament button The ionizer settings can be changed selecting Ionizer from the Head Menu A green status LED on the back panel of the ECU box indicates the emission status of the filament at all times and it provides the fastest way to verify if the filament is emitting electrons 5 Perform an analog scan under the current scan conditions Analog mode is the spectrum analysis mode common to all Quadrupole Gas Analyzers The X Axis represents the mass range displayed in the Mass Spec Parameters menu The Y Axis represents the ion current amplitudes of every mass increment measured RGA starts in the Analog mode of display by default The scan range defaults to 1 to 50 amu e Select Start from the Scan menu or simply click on the toolbar s GO button to trigger an analog scan e After a small delay the analog scan data starts to be displayed on the screen e Rescale the Y Axis clicking on
257. ne bakeouts Turn off the CIS and disconnect the ECU from the probe Wrap a heating tape or heating jacket around the entire probe and cover with fiberglass insulation if necessary Make sure the entire probe including flanges and auxiliary valves is evenly covered Note Isolation and or Pressure Reducing valves placed between the chamber and the probe must be baked out along with the rest of the quadrupole probe Follow the manufacturer s instructions regarding maximum bakeout temperatures for the different valves Bake the quadrupole probe to at least 200 C for several hours i e overnight is usually ideal After bakeout wait for the probe to cool down to room temperature before mounting the ECU back on its feedthru flange Check for the correct operation of the probe and run a complete peak tuning procedure if necessary CIS Quadrupole Gas Analyzer lonizer Replacement 7 7 lonizer Replacement As the CIS Analyzer is used deposits form on the ionizer parts and the sensitivity of the sensor is degraded Once the sensitivity of the spectrometer is significantly affected by this buildup it is necessary to completely replace the ionizer All components of the ionizer should be replaced together at once The replacement procedure is simple and should only take a few minutes Use the exploded view of the CIS Ionizer included in the Probe Assembly chapter of this manual for extra help during the entire replacement procedure It is re
258. needed to perform quantitative measurements with the instrument The formalism presented assumes multiple gas analysis but is equally valid for single gas measurements Please consult the suggested references for details and examples of these procedures The entire mathematical formalism used to derive the partial pressures of a mixture based on a single mass spectrum is based on one assumption The total spectrum is a linear combination of the spectra of the different species that are present in the mixture In other words the total spectrum is equal to the sum of the individual peaks that would be observed if each constituent were alone in the system In mathematical terms the assumption stated above can be written as the following linear equation CIS Quadrupole Gas Analyzer 2 14 Partial Pressure Analysis Basics Hy X hug 1 where is an integer variable that represents the gases present i e assign an integer to each gas starting with one M is an integer variable that represents the mass numbers for the entire mass range of the spectrum Hy total peak height amps of the spectrum at mass number M hme peak height contribution amps from gas g at mass M he is related to the fragmentation pattern the CIS Analyzer s sensitivity and the partial pressure of gas g by the equation hmg Omg S P 2 where Omg Fragmentation factor of gas g at mass M Ratio of ion signal at mass M to the ion signal at the p
259. ng water This water level is one hundred times larger than the 10 Torr corresponding to 1 PPM of water in the process chamber meaning that the water vapor concentration cannot be reliably measured to better than 100 PPM under these very common operating conditions The MDPP limit could be improved to 20 PPM increasing the operating pressure in the RGA chamber to 5 10 Torr during analysis However even a 20 PPM MDPP limit for water is not low enough in many cases The same limitations must be kept in mind for all other potential interfering gases In order for any species to be detectable at the PPM level i e 10 Torr in a 10mTorr process the residual mass spectrum for the PPR must show pressure readings of less than 10 Torr at the mass values corresponding to the peaks of that species Such levels are not easily achieved repeatedly in any vacuum system unless very special precautions are taken to eliminate all sources of contamination The problem is particularly serious for masses under 50 amu where there is always a variety of background peaks in the residual mass spectrum Even though the RGA is intrinsically capable of performing sub PPM measurements it is usually not easy to find places in the residual mass spectrum of the RGA where the background is readily in the PPM levels The MDPP limit for air is usually limited by the compression ratio of the pumping station In the SRS PPR the N levels usually go down to 10 Torr with oxy
260. nit ECU attaches directly to the probe s feedthru flange Its correct alignment to the probe is very important during installation Carefully follow the instructions below to insure proper alignment Warning Failure to follow the installation instructions below could result in damage to the ceramic feedthru connectors of the probe s flange and would require sending the entire unit back to Stanford Research Systems for a complete flange replacement Hardware Requirements External Power source Standard ECU boxes require an external 24 2V DC power supply 2 5 Amps i e 60 Watt to power its electronics Units with the optional built in power module Option 02 plug directly into a wall AC outlet and require no extra power sources 2 Power cables External 24V power supplies must have a cable with a 9 pin type D female connector on the free end wired as described in the ECU 24VDC power connector diagram shown below Note A power cable with a properly wired female DB 9 cable connector is CIS Quadrupole Gas Analyzer Installation 1 9 provided by SRS with all CIS units that do not include the built in power module Option 02 Attach the connector s wires to a longer two wire cable of similar or bigger gauge to make a power cord compatible with the CIS s power connector CIS units with the optional built in power module Option 02 are connected directly to a wall outlet using the three wire power cord provided by
261. nnn Ee ENER 9 16 Electron Multiplier High Voltage Power Supply eee 9 16 CIS Quadrupole Gas Analyzer Overview of the RGA 9 3 Overview of the RGA The SRS RGA is a mass spectrometer consisting of a quadrupole probe and an Electronics Control Unit ECU which mounts directly on the probe s flange The quadrupole probe is a mass spectrometer sensor consisting of an ion source a quadrupole mass filter a Faraday cup and an optional electron multiplier Option 01 Ions are created from the residual gas of a vacuum system by electron impact ionization Ions of a particular mass to charge ratio have stable trajectories through the mass filter depending on the DC and RF voltages applied to the quadrupole rods The selected ions are collected in a Faraday cup or multiplied in an electron multiplier The ECU box 3 x 4 x9 contains all the electronics necessary to operate the RGA It connects directly to the probe s feedthru flange and also to a host computer Its regulated power supplies set the ionizer voltages the filament s electron emission current the high voltage across the electron multiplier and the RF DC levels on the quadrupole filter A logarithmic transconductance amplifier converts ion currents into voltages that are read by an A D converter A microprocessor and control firmware direct the operations of the spectrometer the data acquisition and the communications through the RS232 serial link The el
262. ns A new command must be sent to the spectrometer in order to stop the scanning activity Once the command is received the scan is immediately stopped all transmission is halted and the transmit buffer is flushed all remaining data is lost The stopping command is executed after the scanning ends SCH Do nothing command Commonly used to interrupt continuous scanning mode SCparam param 1 255 Multiple scans The number of scans specified by the parameter is executed Scanning is immediately stopped when a new command is received as in the case of continuous scanning SC The default parameter value is used for multiple scan excecution Default parameter value 1 single scan Error checking Number parameters must be integers and within the specified range No query format is allowed for the parameter Programming Tips e Any command received by the CIS Head while scanning will immediately stop the scan process and clear the transmit buffer Clear the computer s receive buffer to reset the communications The new command which stopped the scan is excecuted e The CIS Head has the ability to store a complete scan in its output buffer The scan remains in memory until all the data is transmitted out to the host computer over RS232 As a result of the high data acquisition rate there might be a delay between the time at which the data is collected and the time at which a complete spectrum is displayed by the host computer The t
263. nt of use Modern day purity requirements usually fall in the ppm and sub ppm levels and immediate response to contamination events is required to minimize costly defects and failures in finished products The closed design of the ionizer is entirely responsible for the low detection limits that are achieved with the CIS Quadrupole Gas Analyzer Ionization takes place directly at the process pressure inside a gold coated anode tube that does not contribute to the background signals The ionizer is also isolated from the rest of the sensor through differential pumping which minimizes the backsteraming of impurities from the quadrupole assembly volume into the ionization region The combination of direct sampling and differential pumping provides the potential for ppm and even sub ppm detection limits for even the most pervasive residual gases A well matched Pumping System combined with careful control of contamination sources is all that is generally required to properly operate the instrument Read the Pumping System Requirements section in the Probe Chapter of this manual for details on pumps specifications Consult Appendix D for information on the application of the CIS Analyzer to PPM Level Gas Analysis In the CIS Mode of operation the electron emission current is reduced to 0 05 mA to bring down the ion densities in the ionizer and minimize signal non linearities in the mTorr pressure range The electron energy can be set to either 35 or 70 e
264. nt wrench for standard hex head bolts and nuts or a 1 4 12 point wrench for 12 point bolt heads Optional adapter flanges Install an adapter flange in the vacuum system if no 2 3 4 CF ports are available Zero Length Adapter flanges with a 2 3 4 CF flange on one side and a bigger size flange on the other are economical alternatives to reducing flange sizes CIS Quadrupole Gas Analyzer Installation 1 7 Procedure 1 Determine the placement of the probe in the vacuum chamber following the instructions listed in step 4 of the Hardware Requirements section 2 Remove the plastic plug from the CIS Mounting Flange See Figure 1 Avoid contamination following good high vacuum practices Do not touch with bare fingers any part of the probe that will be exposed to the vacuum Do not talk directly at an open vacuum port 3 Hold the probe in a secured upright position and do a thorough visual inspection of the part Check for loose damaged or misaligned components Check the integrity of the knife edges in the exposed CF flanges Important Abort the installation procedure and contact SRS immediately if the probe appears damaged in any way 4 Position the copper gasket and attach the CIS probe to the vacuum system Avoid scratching the vacuum seals and do not use non metal gaskets Check the correct orientation of the Pumping System Port before bolting things down Tighten the bolts according to the standard tightening procedure for
265. nts The input offset voltage of the I V converter s op amp is nulled prior to calibrating the converter s gain This is done by strobing the MISC port bit LINEAR high which activates the relay U702 configuring the op amp to a linear amplifier with a gain of 1001 for it s own input offset voltage The CPU then adjusts OFFSET to null the output of the op amp nulling it s input offset voltage The I V converter is returned to the log mode by strobing the LOG bit high A second and identical I V converter resides next to the I V converter described above The second I V converter is operated and calibrated in the exact same manner however collected ion currents are not applied to its input The primary purpose of the second channel is to correct the output of the first I V converter against temperature effects CIS Quadrupole Gas Analyzer 9 16 Description of Schematics Schematic name QMSE V2 Electron Multiplier High Voltage Power Supply The electron multiplier option extends the operation of the RGA to much lower pressures By multiplying the ion current before detection in the I V converter the signal to noise ratio is not affected by the bias current noise of the I V converter Since the gain of the electron multiplier varies rapidly with applied bias well regulated negative high voltage supply is required A switching power supply synchronized to a sub multiple of the master clock at 43 2 kHz followed by a voltage multiplier is
266. of the electrometer are listed in a table in the Electrometer section of the Electronics Control Unit chapter The command execution time includes some initial time spent waiting for the Quadrupole Mass Filter and the electrometer response to settle As usual a compromise must be made between signal to noise and measurement time The ion current is expressed in the usual format 4 byte long 2 s complement integer in units of 10 A with Least Significant Byte transmitted first Important e During a Single Mass Measurement the spectrometer performs a Miniscan around the mass requested and the maximum current value measured is sent out over RS232 The scanning procedure referred to as Peak Locking is designed to measure peak currents for individual masses in a mass spectrum without being affected by drifts in the mass scale calibration The Miniscan covers a 0 6 amu range centered at the mass requested and selects the maximum current from 7 individual measurements performed at 0 1 amu mass increments e The detector settings i e type of detector and noise floor setting to be used during the measurement must be selected in advance with the NF and HV commands otherwise the measurements are performed with the detector settings that are present at the time the scan is triggered e The ion detector can be zeroed prior to the measurements performing an analog or histogram scan or using the CA command under the same detector set
267. of air due to a leak An overnight bake out of the vacuum system reduces the total pressure to 0 2 x 10 mbar 0 1 x 10 mbar is water and 0 1 x 10 mbar is air Is the vacuum system cleaner than before the bakeout If the process or experiment is sensitive to oxygen the system is no cleaner than before the bakeout Second the assumption fails because total pressure measurement is not very precise measurements more precise than 10 are difficult and expensive If a system is operating at a standard pressure of 1 0 x 10 mbar and the next day the pressure is 1 1 x 10 mbar would there be cause for concern The vacuum system could be filled with 1046 oil vapor or the pressure gauge sensitivity could have changed 10 The RGA is designed to address exactly these types of questions by immediately showing the user what is in their vacuum system The primary application of the RGA is to analyze the composition of a vacuum system The composition can be used to detect impurities monitor gas fills or analyze ongoing chemistry Another application of the RGA is as a leak detector It serves this use very well and in many ways is superior to a portable helium leak tester In the remainder of SRS Residual Gas Analyzer 2 Appendix A this application note we will illustrate the usefulness of an RGA The data shown are real results from experiments designed to illustrate certain points SRS Residual Gas Analyzer Appendix A 3 Composition Analysis T
268. ole Gas Analyzer Scan and Measurement Commands 5 45 The precision and duration of the measurement are totally determined by the NF parameter value The scan rates and signal to noise ratios for the different NF settings of the electrometer are listed in a table in the Electrometer section of the Electronic Control Unit chapter The command execution time includes some initial time spent waiting for the Quadrupole Mass Filter and the electrometer response to settle As usual a compromise must be made between signal to noise and measurement time The ion current is expressed in the usual format 4 byte long 2 s complement integer in units of 10 A with Least Significant Byte transmitted first Important e During a Single Mass Measurement the CIS Head performs a Miniscan around the mass requested and the maximum current value measured is sent out over RS232 The scanning procedure referred to as Peak Locking is designed to measure peak currents for individual masses in a mass spectrum without being affected by drifts in the mass axis calibration The Miniscan covers a 0 6 amu range centered at the mass requested and selects the maximum current from 7 individual measurements performed at 0 1 amu mass increments e The detector settings i e type of detector and noise floor setting to be used during the measurement must be selected in advance with the NF and HV commands otherwise the measurements are performed with the detec
269. on limits are pre programmed by the NF Noise Floor setting current value is transmitted for MI and after each mass increment through MF for a total of MF MI SA 1 measurements See AP query command The ion currents are represented as integers in units of 0 1 fA and transmitted directly in Hex format four byte integers with 2 s complement format and Least significant byte first The type of detector and noise floor settings to be used during the scans must be selected in advance with the NF and HV commands Important e Any command received by the CIS Head in the middle of a scan will immediately stop the scan halt transmission and clear the transmit buffer e The detector s zero and the internal scan parameters are checked and corrected at the beginning of each scan resulting in a slight delay before the scan actually starts e An extra current value unrelated to the scan is transmitted out to the host computer at the end of each analog scan Please see AP and TP Commands The current value does not need to be porocessed or displayed but it needs to be accounted for by the software communicating with the CIS Head CIS Quadrupole Gas Analyzer 5 48 Scan and Measurement Commands e Unless otherwise specified the measurements are performed with the detector settings that are present at the time the scan is triggered Parameters SC Continuous scanning mode The CIS Head produces a continuous string of analog sca
270. onding change in partial pressure of the gas from which the ion is produced The correspondence might be represented graphically or as a table of values See also Sensitivity Space charge The electrical charge carried by a cloud of free elctrons or ions Space charge can causes serious changes in the potential distributions of the ionizer and ultimately limits the pressure operating range of all RGA s Total Pressure The average normal force per unit area exerted by all the gas molecules impacting on the internal surfaces of the vacuum chamber Units are typically Torr mbar or Pascal Note The SRS RGA is capable of collecting total ion currents that can be turned into total pressure measurements with the help of gas dependent total pressure sensitivity factors UHV Abbreviation for Ultra High Vacuum Pressure 10 Torr SRS Quadrupole Gas Analyzers
271. one of the fault conditions that can be internally detected by the CIS Head The Error Codes are used only by the RGA Windows program to report all internally detected errors This section lists causes and troubleshooting procedures for all the possible Error Code values available in the CIS Analyzer Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting DETI Electrometer Electrometer Error OP AMP Input Offset Voltage out of range A large offset input voltage is present in one or both of the I V converter op amps This problem results in electrometer calibration errors and will cause erroneous ion current readings Contact SRS DET3 Electrometer Electrometer Error COMPENSATE fails to read 5nA input current The logarithmic output of the temperature compensating picoammeter is not within the levels expected for a 5 nA input current Contact SRS DET4 Electrometer Electrometer Error COMPENSATE fails to read 5nA input current The logarithmic output of the temperature compensating picoammeter is not within the levels expected for a 5 nA input current Contact SRS DETS5 Electrometer Electrometer Error DETECT fails to read 5nA input current The
272. ong have a 0 250 diameter 100 pin tolerance and are held in quadrature and parallel to each other to tolerances better than 300 uin by the precision ground alumina spacers Spring loaded perforated screws fasten the rods to the spacers The whole assembly is self aligning can easily be taken apart for cleaning and it can withstand repeated cycling to 350 C for bakeout The exact placement of the rods is optimized to minimize the distortion of the electrodynamic quadrupole field by canceling higher order multipole potential terms The radius of the circle inscribed by the rods is 0 109 The frequency of operation is f 2 7648 MHz CIS Quadrupole Gas Analyzer 3 10 Quadrupole mass filter Principle of operation The following figure schematically represents the quadrupole mass filter and its connections Guadrupale axis 27 P DU bi E EN L Ma casct U COS wt Figure 5 Quadrupole Connections During operation a two dimensional X Y quadrupole field is established between the four cylindrical electrodes with the two opposite rods connected together electrically Ions enter the filter along the Z axis and start oscillating in the X and Y directions The ions are separated based on their mass to charge ratio by lateral forces resulting from the electric potentials applied to the rods A combination of DC and RF voltages control the quadrupole filter operation Successful separation of a specific mass species requires s
273. onitored in the same fashion as the channels above SRS Residual Gas Analyzer 2 Appendix C Valid Outputs 1 output channel 1 TTL signal is used to indicate that the table channel outputs are valid This signal is set High while the RGA is scanning after completion of the first scan and set low as soon as the scan is stopped the output card must be enabled Manual Outputs 10 output channels 10 TTL signals are mapped so that the user can directly set them Low or High manually from a dialog box in the RGA program The use of these outputs is left to the discretion of the user Hardware requirements TTL I O card Required The TTL I O card is a 24 bit Input Output card that is mapped directly into the PC I O space no IRQ is required An installation diskette is shipped with each card to help the user install and test the card The installation diskette is essential since it installs files that the RGA program requires The I O card is installed in the same PC where the RGA program is running so an empty 8 bit or 16 bit expansion slot is required in that computer A 37 pin D Connector cable is shipped with the card to allow access to the signals All signals are active high initially low Electromechanical Relay board optional This 24 relay board is available as an option and is 10096 compatible with the I O board mentioned above The cable shipped with the I O board connects directly to the relay board The relay board is s
274. onment 10 mTorr and ions are produced by electron impact directly at the process pressure The ions enter the quadrupole through the small aperture available A pumping system attached to the Pumping System Port of the CIS Cover Tee keeps the filament and the rest of the quadrupole mass spectrometer at pressures below 10 Torr through differential pumping The closed design of the ionizer enhances the signal from the sample gas relative to the signals arising from the background gases present in the analyzer and is directly responsible for the sub ppm detectability limits that are attainable with the CIS Analyzer CE Cover Tee Luechupole Mase Alter Se A CIS Mounting Fangs Side Port for Turbo Fum p Ate chin ent Figure 2 Cross section of the Closed Ion Source CIS 1 Repeller 2 Filament 3 Ionization Tube Anode 4 Alumina insulator and seal 5 Spring washer 6 Emission Slit 7 Alumina insulator and seal 8 Exit plate 9 Exit aperture CIS Quadrupole Gas Analyzer 2 6 Basic Data Acquisition Modes The mass filter determines which ions reach the detector at any given time It is operated by a combination of RF and DC voltages and the filtering action is based on the mass to charge dependency of the ion trajectories on the RF and DC fields The magnitude and frequency of the RF determine the mass to charge ratio of the ions that can pass through the filter without striking the rods i e with stable oscillations T
275. onnected to a pressure reducing gas inlet system does an excellent job sampling gases at pressures 10 Torr However even though most of the commercially available RGA s have adequate sensitivity and dynamic range to detect PPM level contaminants in principle interferences from process gases and background interferences from the sensor itself can make the detection of PPM levels of impurities difficult in practice The two basic sources of interference that are observed in PPR systems are Background interference The background gases present in the analyzer chamber can obscure the MDPP s of many important gases particularly H2 H20 N2 CO and CO Background gases are due to outgassing electron stimulated desorption and the finite compression ratio of the pumping system In order to best illustrate the limitation in MDPP levels lets consider as an example the analysis of water in a 10 Torr Ar sputtering process During process monitoring the mass spectrometer typically runs at about 10 Torr corresponding to a three decade reduction factor across the low conductance path of the PRGIS The pressure drop brings a 1 PPM of water in the process chamber to a partial pressure in the mass spectrometer of about 10 Torr well within the detection limit of a typical RGA However with the mass spectrometer isolated form the process gases the residual pressure in the PPR chamber is at best in the order of 10 Torr with most of that bei
276. or e Theratio of this output signal to the pressure of the gas is the sensitivity factor S g During these measurements it is very important to insure that the partial pressures of all other gases in the system are small enough so that they may be neglected The sensitivity factors calculated can only be applied to situations where the CIS Analyzer is used with the same operating parameters See the Sensitivity Tuning section in the Tuning chapter of this manual for more details on this calibration procedure The underlying assumption when using sensitivity factors in quantitative calculations is that there is a linear relation between the partial pressure and the corresponding CIS Analyzer signals of the gases Deviations from linearity are to be expected above certain pressure values due to space charge effects in the ionizer and ion neutral scattering interactions in the filter A more thorough check of the CIS Analyzer s sensitivity involves measuring the ion signals over several orders of magnitude of partial pressure to determine the range over which a linear relationship exists The sensitivity factor for the gas is calculated as the slope of the signal vs partial pressure response over the linear range RGA Windows uses three sensitivity factors stored in the non volatile memory of the CIS Head The sensitivity factors one for RGA Mode of operation and two for the two different values of electron energy i e 35 and 70eV in the CIS
277. or additional help CIS Quadrupole Gas Analyzer 8 10 Built in Hardware Checks Built in Hardware Checks Several firmware driven hardware checks are built into the CIS Head Some checks are automatically performed as soon as the unit is powered up i e Power on checks and others are activated when the emission from the ionizer is turned on i e filament s Background Protection Mode Most of the checks can be triggered by query commands i e Error Reporting Commands at any time This section describes the internal checks based on the hardware components they test The information presented includes e The type of check performed e The Status bit affected See Error Byte Definitions e The specific Error Byte affected See Error Byte Definitions e The query command that can be used to trigger the check see Error Reporting Commands e The prefix of the Error Codes associated to the check e Is this a Power on check 24V DC Power Supply STATUS Bit affected 6 Error Byte affected PS_ERR Error Reporting Command EP Error Codes prefix PS Power on check Yes The output of the external 24 V DC Power Supply must be between 22 and 26 Volts at all times while the instrument is in operation Its voltage level is automatically tested when the instrument is turned on and can be checked at any time with the query command EP The same test is performed in units with built in power modules Option 02 to check the voltag
278. or is rarely used to measure partial pressures below 10 Torr in the CIS Analyzer At pressures below that value the CDEM option becomes a much better alternative allowing for faster scan rates and improved signal to noise ratios The best characteristics of FC detection are simplicity stability large dynamic range and lack of mass discrimination AIl ions are detected with the same efficiency regardless of their mass The ECU automatically connects the FC electrode to the electrometer input upon power on reset and whenever the electron multiplier is not turned on Electron Multiplier Operation An Electron Multiplier is recommended for all CIS Analyzers particularly when sub ppm detectability is required from the instrument or when pressures under 10 Torr are routinely sampled Macro Multi Channel Continuous Dynode Electron Multipliers are used in the SRS CIS Analyzers fitted with the electron multiplier option Option 01 They consist of a straight four channel tube made out of a special resistive glass i e high secondary electron emission yield with a cone of the same material attached to the front end The extruded channels run along the length of the device and are twisted at the time the part is drawn to eliminate ion feedback Each CDEM is placed upright next to the FC and away from the line of sight of the ionizer 1 e off axis configuration When the cone is biased negatively 1000 to 2500V relative to the back end posit
279. ore declaring a hardware problem Parameters This command is a query and can only have one parameter format EP Error checking The only acceptable parameter is a question mark The absence of a parameter i e EP is treated as a bad parameter error Description QMF ERR Byte Query Echo QMF ERROR Byte Query the value of QMF ERR and update its value after running a fresh check on the Quadrupole Mass Filter s RF Power Supply Bit4 of STATUS and the QMF ERR byte are updated based on the tests results The QMF ERR byte value is returned to the computer in ASCII format and with a lt LF gt lt CR gt terminator No errors are present as long as the byte value is zero Consult the Error Byte Definitions section of this chapter for detatils on the different error bytes of the CIS Analyzer CIS Quadrupole Gas Analyzer 5 58 Error Reporting Commands ER Consult the Troubleshooting chapter of this manual for possible causes and solutions to any problems reported Always try the query a second time before declaring a hardware problem Parameters This command is a query and can only have one parameter format EQ Error checking The only acceptable parameter is a question mark The absence of a parameter i e EQ is treated as a bad parameter error Description STATUS Byte Query Echo STATUS Byte Query the value of the STATUS Error byte The STATUS byte value is returned to the computer in ASCII format and with a
280. ote In the SRS RGA the Ion Energy is equal to the voltage biasing of the anode grid in Volts and has two possible settings i e Low and High Ionization The process that results in the formation of ions from neutral atoms or molecules During ionization electrons are added or removed from the molecules to form negative or positive ions respectively Note In the SRS RGA the ionization is caused by electron bombardment outer electrons are removed by the impact of energetic electrons on the molecules Ionization efficiency The ionization probability normalized to the probability of ionization of a reference gas Ionization Potential The minimum energy per unit charge often in eV required to remove an electron from an atom or molecule to infinite distance Note In the SRS RGA the Electron energy must be set above the ionization potential of the molecules for ionization to occur Ionization probability The number s of ion pairs equal amounts of positive and negative charges appear as ions produced by an electron traveling a unit ditance typically 1 cm through a gas at unit pressure typically 1 mTorr It depends on the ionization potential of the electrons used for bombardment Ionizer Probe Component The portion of the mass psectrometer probe that generates the ions and accelerates them as a beam Note The components of the SRS RGA ionizer are anode grid repeller focus plate and filament Linearity The extent to whic
281. ource Quadrupole Gas Analyzer The CIS Analyzer is available in three different models with mass ranges of 1 to 100 CIS100 1 to 200 amu CIS 200 and 1 to 300 amu CIS300 All models operate in the Constant Resolution or Constant Am mode with AMios preset to one amu nominal at the factory The operating pressure is UHV to 10 Torr for all models A complete product specifications listing is included in the introductory sections of this manual CIS Quadrupole Gas Analyzer Basic Data Acquisition Modes 2 5 Basic Data Acquisition Modes The SRS CIS Analyzer is a mass spectrometer that analyzes gas mixtures by ionizing some of the gas molecules positive ions separating the resulting ions according to their respective masses and measuring the ion currents at each mass Partial pressure measurements are determined with the help of previously calculated sensitivity i e calibration factors by reference to the abundance of the individual mass numbers attributed to each gas type Principles of operation During analysis positive ions are formed within the ionization volume and directed towards the spectrometer s quadrupole mass filter The type of ionizer used in the CIS Analyzers is referred to as a closed ion source CIS The CIS sits on top of the quadrupole mass filter and is simply a short gas tight tube with two very small openings for the entrance of electrons and the exit of ions The source is exposed to the process envir
282. outgassing is a frequent interference and especially important because it is a serious source of contamination in many high vacuum processes Overnight bakeouts at gt 200 C are the best option to minimize water outgassing from an OIS RGA H outgassing from the OIS electrodes is only a concern for users operating in the UHV regime Hz is dissolved in most varieties of SS300 and readily outgasses from the hot OIS electrodes contributing to the background signals for the gas Electron Stimulated Desorption ESD Even after an RGA has been thoroughly baked out peaks are frequently observed at 12 16 19 and 35 amu which are formed by ESD from surfaces within the OIS rather than by electron impact ionization of gaseous species ESD affects the RGA performance in a way similar to regular outgassing Several steps can be taken to minimize the effect e Degassing with high electron energies e Gold plating the ionizer decreases the adsorption of many gases and hence reduces the ESD effect Using platinum clad molybdenum ionizers is another alternative e Reducing the extent of the electron beam e Reducing the surface area of the OIS For example use wire mesh instead of solid perforated metal e Avoid contaminating the ionizer Background interferences The quadrupole mass filter assembly has a large surface area in comparison to the ionizer and even though it does not get as hot as the ionizer during operation it still outgasses The fact that t
283. ox RS232 LED RS232 Activity indicator that flashes whenever a character is received or transmitted over RS232 Error LED The Error LED flashes on off a couple times when an error such as an illegal command or parameter has been detected CIS Quadrupole Gas Analyzer 5 6 Command Syntax Command Syntax The CIS commands are ASCII character strings consisting of a two letter case insensitive command name a parameter and a carriage return terminator Note The carriage return character decimal ASCII value 13 is represented throughout this manual with the symbol CR All command strings must be terminated with this character in order to be acknowledged by the CIS Head Valid parameters are Numbers Numbers are the most common type of parameter used to program the CIS Analyzer Number parameters must be within a command specific range and must not conflict with any pre existing parameter values of the head Only decimal format is accepted The fractional parts are truncated to four decimal places before being stored in memory The sign is optional for positive numbers A zero in front of the period is optional in fractional numbers with magnitude less than one Asterisk default A single asterisk indicates that the default parameter value stored in the CIS head s permanent memory is to be used for command execution The asterisk must be strictly followed by a CR Question mark Query Query commands
284. pendability in mass spectrometry applications However in order to achieve maximum useful lifetime and optimum performance it is very important to handle them very carefully Please read the CDEM Handling and Care section in the Maintenance chapter of this manual to familiarize yourself with some of the basic procedures that must be followed for the correct operation of the multipliers Upgrading to an Electron Multiplier Detector An Electron Multiplier upgrade Option 01 to the standard Faraday Cup FC detection setup is highly recommended for all CIS Analyzers particularly when sub PPM detectability is expected from the instrument or when pressures under 10 Torr are routinely sampled The detector upgrade consists of a state of the art Macro Multi Channel Continuous Dynode Electron Multiplier CDEM and a negative high voltage power supply 0 to 2500V The advantages of operating the CIS Analyzer with a CDEM detector are more easily illustrated through examples Example 1 In the RGA mode of operation the best detection limits that can be expected from a CIS Analyzer operated with a FC detector are in the order of 10 Torr Modern day pumping systems with dry pumped turbo pumps can easily evacuate chambers down to the 10 Torr level making it impossible for the CIS Analyzer to provide a detailed partial pressure analysis of the residual gas with the FC detector Operation of the electron multiplier at gain levels above 100X and und
285. placement of the filament tabs on the posts and a stainless steel screws hold the wire in place 11 Remove the two screws that hold the filament in place and pull the filament with its tabs out the ionizer assembly Discard the old filament CIS Quadrupole Gas Analyzer 7 12 Filament Replacement 12 13 14 15 16 17 18 Open the filament box and pick up a new filament by one of its tabs with the clean tweezers Very carefully mount the filament on the mounting posts so that the square washers fall into the slots The filament wire should line up with the anode slit Fasten the filament in place using two new screws The filament wire is pressed between the post and the square washer Visually inspect the filament alignment and do any adjustments that might be necessary The filament should be perfectly straight and centered on the anode slit Misalignments result in reduced ionization efficiency and need to be corrected before the probe is mounted back on the vacuum system Reattach the repeller plate to the filament post using a fresh screw and inspect visually the entire ionizer assembly to assure the correct alignment of its parts Once satisfied mount the probe back on the vacuum system The anode tube should easily slide into the alumina seal Check the correct rotational orientation of the feedtrhu flange i e same as it was before disassembly before tightening the flange bolts A bakeout of the probe i
286. ponent Ionizer s electrode plate that serves the double purpose of drawing the ions away from the anode grid and containing the ionizing electrons inside the source Fragment ion An ion of mass smaller than that of the original parent molecule Fragmentation factor The fragmentation factor of gas g at mass M is defined as the ratio of ion signal at mass M to the ion signal at the principal mass peak of gas g Fragmentation of molecules The breaking of multi atomic molecules into units of fewer atoms some of which are usually electrically charged Fragmentation or cracking pattern The fragment distribution of ionic species which results from dissociation and ionization of multi atomic molecules of given species in the ionizer Head also RGA Head The combination of the Probe and the Electronics Control Unit SRS Quadrupole Gas Analyzers Glossary of Terms 3 Inert Gas A gas that does not normally react chemically with other substances Example He Ar Kr and Xe Typically used for calibration purposes in RGA s Ion An atom or molecule which has gained or lost one or more electrons and therefore has a negative or positive charge Note Most RGA s use electron bombardment to ionize molecules and detect only positive ions Ion current The rate of ion flow into the detector Usually expressed in units of amps Ion Energy The kinetic energy of the ions as they move down the quadrupole mass filter and expressed in eV N
287. probe In some cases i e depending on the vacuum composition replacement of the parts might be the only solution to a contamination problem CIS Quadrupole Gas Analyzer Probe Bakeout 7 5 Probe Bakeout Bakeout of the CIS probe is recommended in the following cases 1 After installation of the probe in the vacuum chamber 2 After any prolonged exposure of the probe assembly to open air 2 When background contamination is present in the mass spectra 3 When the performance of the CIS is degraded due to excessive contamination When a new part is introduced into a high vacuum system or after the vacuum chamber has been vented up to air outgassing of molecules particularly H20 from the walls usually sets the time it takes the pumping station to achieve the desired base pressure A bakeout accelerates the outgassing rates and results in reduced pump down times A thorough bakeout helps clean the entire probe and usually results in reduced contribution of the quadrupole sensor to the background signals Routine overnight bakeouts are required for CIS Analyzers used in the detection of trace level impurities and are essential for applications requiring the determination of ppm levels of water For example the detection of 1ppm of water in 1 mTorr of process gas is best achieved in the pressence of background water levels in the order of 10 Torr Such water pressures can only be achieved overnight after a complete probe bakeout As
288. quadrupole mass spectrometer fitted with an electron multiplier makes the CIS Analyzer an extremely versatile system for on line process monitoring and control verification of process gas purity at the point of use high vacuum residual gas analysis and process equipment leak checking The user can easily switch between the above applications by simply selecting one of two basic CIS Operating Modes The two modes of operation correspond to different ionizer settings and can be easily selected from the RGA Windows software The following table describes the ionizer parameter settings for both modes of operation CIS Parameter Programmable RGA Mode CIS Mode range Electron emission current mA 0to1 0 5 0 05 Electron energy eV 25 to 105 70 70 or 35 Ion Energy eV 4or8 8 8 Extraction Voltage V 0 to 150 40 typical 40 typical Sensitivity for N2 28 amu 10 A Torr 10 A Torr Linear range upper limit Torr 10 2 10 MDPP Torr Faraday Cup Detector CDEM Detector Table notes The CIS tests were performed using a 70 L s hybrid turbo pump backed up by a high performance diaphragm pump RGA Mode UHV P 10 Torr In the RGA mode the CIS Analyzer is exposed to pressure levels below 10 Torr and used for high vacuum residual gas analysis and process equipment leak checking This mode is used for example during the first stage of a sputtering process when the chamber is evacuated to
289. r a variety of purposes Make sure the CIS Analyzer is powered up and ready to go Check the quality of the serial connection to the host computer Check the user s communication software to make sure it is communicating CIS Quadrupole Gas Analyzer 5 12 Programming the CIS Head properly with the spectrometer Check the serial numbers of the CIS heads connected to the computer s serial ports Programming the lonizer Positive ions are produced in the closed ionizer by bombarding process gas molecules with electrons derived from a heated filament The operational parameters that affect the efficiency of the ionizer are electron energy ion energy electron emission current and extraction voltage The CIS ionizer is typically operated under one of two basic set of parameters corresponding to the two Basic Operating Modes of the Analyzer Please consult the Basic Operating Modes section in the General Operation chapter of this manual for details The Ionizer Control Commands program all the ionizer voltages and turn the filament on off The STATUS byte is transmitted at the end of their execution Important The Repeller plate and the extraction plate are only biased while the filament is emitting electrons The anode tube is electrically biased at all times Setting the ionizer parameters The following list of commands will set the electron energy to 70 eV ion energy to high 8eV extraction voltage to 50V and it will then turn the fi
290. r conditions are accounted for e The values of the Error Bytes often change after an Error Byte query command is executed Some query commands update the byte value after performing a fresh test on the hardware while others clear error bits after they are read to provide a clean error reporting slate Please see the Error Reporting Commands list for details e Itis good programming practice to check the value of the STATUS byte whenever it is returned at the end of command execution e In cases were a hardware error is reported at the end of a command attempt the command one more time before declaring a hardware problem CIS Quadrupole Gas Analyzer CIS Command Set 5 27 CIS Command Set This section lists and describes the commands in the CIS Command Set The commands are separated into several lists based on their functions They are each identified by a header that describes the command s syntax with the acceptable parameter values the command s function and the information returned Echo to the computer during execution The CIS commands are ASCII character strings consisting of a two letter case insensitive command name a parameter and a carriage return terminator Note The carriage return character decimal ASCII value 13 is represented throughout this manual with the symbol CR All command strings must be terminated with this character in order to be acknowledged by the CIS Head The two letter mnemonic in ea
291. rection factor is then automatically used by the firmware to offset correct all ion currents measured under the same detector settings The detector settings are the electrometer s noise floor parameter value and the type of detector 1 e FC or CDEM in use at the time the zeroing is performed Offset correction factors for all the possible combinations of detector settings can be generated and accumulated in the head s memory However all offset correction factors are cleared after a recalibration CL of the electrometer is performed and when the unit is turned off Please consult the CIS Command Set section for details on the CL and CA commands CIS Quadrupole Gas Analyzer Mass Filter Power Supply 4 11 Mass Filter Power Supply All the necessary electronics required to power up the quadrupole mass filter during mass measurements are built into the ECU box The RF DC levels for each mass are set and regulated from the ECU under microprocessor control and based on internal calibration parameters permanently stored in non volatile memory The difference between the three CIS Analyzer models CIS100 CIS200 and CIS300 is given by the maximum supply voltage available to the rods For example the maximum RF amplitude delivered to the probe in the CIS300 is 1284 V 2568 Vpp and corresponds to ions with mass of 300 amu 8 56 Vpp amu The corresponding DC potential is a maximum of about 430 VDC for masses of 300 amu 215 Vdc on one rod pair
292. rent parameter value to recalculate the internal scan parameters used to step the RF during scans and single mass measurements This is often used to compensate against small temperature drifts in the mass scale caused by drifts in the output of the RF Driver CIS Quadrupole Gas Analyzer Tuning Commands 5 63 Error checking The absence of a parameter i e RI is treated as an error in the parameter This parameter is protected by an internal calibration jumper JP100 and a Protection violation error will result if the jumper is in the Calibration Disabled mode see CE command RSparam param 600 0000 1600 0000 none Description RF Driver output 128 amu Peak Position Tuning command JP100 Jumper protected Echo Query Response Warning Please read the Peak Tuning Section of the Tuning Chapter before using this command Program the output of the RP Driver 128 amu during a Peak Position Tuning Procedure The parameter one of four peak tuning parameters represents the voltage output selected for the RF Driver 128 amu in mV The magnitude of the RF determines the mass to charge ratio of the ions that can pass through a quadrupole mass filter without striking the rods i e with stable oscillations A linear relationship between mass and RF amplitude is one of the most attractive features of these type of filters The regulated output of the RF source that powers the quadrupole rods is controlled by an
293. ressures a variable reduction is required Suitable variable leak valves are available but are significantly more expensive than a fixed aperture Another method of increasing the dynamic range and data acquisition rate is to use an RGA with an electron multiplier The electron multiplier provides gains up to 10 and lowers the MDPP to under 10 mbar This lower MDPP allows the RGA to provide large dynamic range even at low operating pressures A high operating pressure or throughput of the aperture at the RGA also improves the signal to background ratio In this context signal is the gas that is drawn through the aperture and background is outgassing from the system plus backstreaming through the turbo pump The ultimate vacuum of many turbo pump packages is about 10 mbar SRS Residual Gas Analyzer Appendix B 3 The outgassing background will be mostly hydrogen water and nitrogen The backstreaming background will be air If measurements are being made near these background peaks the operating pressure should be kept as high as possible The background can be minimized by designing the tubing such that the effective pumping speed at the RGA ionizer is as high as possible Figure 2 shows two layouts that both have the same signal level The layout with the RGA at the end of a small tube has a small effective pumping speed and will show a larger background level SRS Residual Gas Analyzer 4 Appendix B Signal GOOD Backgroun
294. rincipal mass peak for gas g Sg CIS Analyzer s partial pressure sensitivity factor for gas g in amp Torr see Partial Pressure Sensitivity Factor below P Partial pressure of gas g in the system Equations 1 and 2 are combined to obtain the system of equations Hy E S Ome P 8 Since all gases have more than one peak in their fragmentation pattern the number of peaks M in a real spectrum is generally larger than the number of gases g As a result the system of equations 3 usually has more equations than unknowns This situation is sometimes simplified eliminating some of the extra equations however the best results are obtained using all the equations and a multiple linear regression procedure to calculate the best possible fit to the data Obviously accurate results can only be obtained if the constants Omg and S g are well known for the analyzer being used Note The Analyze Utility of RGA Windows uses a multiple linear regression algorithm as mentioned above to automatically calculate the composition of a typical residual gas environment at the end of any 1 50 amu spectral scan Please see the RGA On Line Help files for details CIS Quadrupole Gas Analyzer Partial Pressure Analysis Basics 2 15 Standard fragmentation patterns for example the fragmentation patterns included in the RGA Library of RGA Windows can be used as a source of us values in moderately quantitative determinations However
295. rom the ionizer replacement kit to mount the new extraction plate on the alumina spacer Slide the bottom alumina ring into place and attach the new anode tube assembly right on top of it Do not forget to reattach the short alignment rod to its bottom plate Use the new screws to fasten its bottom plate to the alignment and connecting rods Once the anode tube is secured in place with two new e clips insert the top alumina ring and reattach the filament mounts Make sure that the alignment rods are back in place and that the filament posts are correctly lined up relative to the anode slit At this point there should be an empty hole that goes all the way through the alumina rings Place the last alignment rod into it and use a fresh e clip to secure it in place Replace the filament following the steps described in the Filament Replacement section of this chapter It is highly recommended that a new filament be used for this step since damage to the delicate wire is usually unavoidable during removal Attach the new repeller plate to the filament post using a fresh screw and inspect visually the entire ionizer assembly to assure the correct alignment of its parts Once satisfied mount the probe back on the vacuum system The anode tube should easily slide into the alumina seal Check the correct rotational orientation of the feedtrhu flange i e same as it was before disassembly before tightening the flange bolts A bakeout of the pro
296. rror checking The absence of a parameter i e DI is treated as an error in the parameter This parameter is protected by an internal jumper JP100 and a Protection Violation error will result if the jumper is in the Calibration Disable mode See CE command DSparam param 0 8500 0 8500 Description DS Parameter adjust Peak Width Tuning command JP100 Jumper protected Echo Query Response Important CIS300 DS range 0 850 40 850 CIS200 DS range 1 2750 41 2750 CIS100 DS range 2 5500 42 5500 Program the value of DS during the Peak Width Tuning Procedure The parameter one of four peak tuning parameters represents the DS value in units of bits amu Warning Please read the Peak Tuning Section of the Tuning Chapter before using this command CIS Quadrupole Gas Analyzer Tuning Commands 5 61 The CIS Head adjusts the DC levels of the quadrupole filter during measurements so that constant mass resolution is automatically available throughout the entire mass range of the spectrometer The bulk of the DC voltage is supplied by a DC power supply whose output is linearly related to the RF amplitude The rest of the DC voltage DC Tweek is provided by the output of an 8 bit digital to analog converter DAC The firmware uses two Peak Tuning Parameters DI Intercept and DS Slope stored in the non volatile memory of the CIS Head to calculate the 8 bit settings of the DAC according to the linear equation
297. rtually identical to those obtained with standard RGA s The 35eV setting is used during process monitoring to eliminate process gas interference peaks A good example is the elimination of the doubly ionized AUT peak that interferes with water detection at 18 amu in sputtering processes Different electron ionization energies are often used to selectively ionize species in a gas mixture High Pressure Sampling with a CIS Analyzer 10 Torr lt P lt 10Torr CIS Analyzers can usually sample gases directly up to about 10 Torr pressure levels The upper pressure limit is set by the reduction in mean free path for ion neutral collisions which takes place at higher pressures and results in significant scattering of ions and reduced sensitivity However operation is not limited to the analysis of gases at pressures below 10 Torr Higher gas pressures can be sampled with the help of a differentially pumped pressure reducing gas inlet system PRGIS just as it is done with conventional RGA s A pressure reducing gas inlet system matched to the conductance of the CIS analyzer will allow the sensor to sample gas pressures as large as 10 Torr As in the case of the PPR systems the penalty paid is reduced sampling speed at the sample inlet and possible memory effects at the ionizer However these problems can be usually eliminated by the addition of bypass pumping in the ionizing region as the process pressures start to get large Conclusions Strict
298. ructions in this chapter to insure that the optimum performance of the instrument is not compromised during the installation process Do not start the installation process until all the necessary hardware components are available Follow good high vacuum practice Set aside a clean dust free work area next to the vacuum chamber before installation begins Do not remove the plastic plugs from the CIS probe ports until moments before the analyzer is ready to be installed in the vacuum system Handle all vacuum hardware components with extreme care A pumping system is required to complete the installation of the CIS Analyzer An oil free turbo pump based pumping system compatible with the CIS Analyzer is available directly from Stanford Research Systems Option O100TDP If a pumping system is already available unpack and or check its integrity before the installation process begins Consult the Pumping System Requirements section in the Quadrupole Probe chapter of this manual for more information on this subject For applications requiring the direct sampling of gas pressures gt 2mTorr a Pressure Reducing Gas Inlet System placed between the gas chamber and the CIS ionizer is required to complete the installation of the CIS Analyzer If a Pressure Reducing Gas Inlet System is already available unpack and or check its integrity before the installation process begins Otherwise Gas Inlet systems for several different pressure ranges can be
299. rupole mass filter QMF and centers its pass band at any mass number within the available range It is included for the convenience of users who wish to use the spectrometer as a mass filter The QMF is parked at the mass requested but no actual measurements take place The command s parameter can be a real number and the step resolution is 1 256 amu The command execution involves two steps 1 The RF DC levels corresponding to the mass requested are calculated and set on the QMF rods based on the mass axis calibration parameter values specified by the last Peak Tuning procedure 2 Afirmware driven algorithm is then automatically enabled to stabilize the voltage output of the RF Driver s controller against temperature fluctuations CIS Quadrupole Gas Analyzer Programming the CIS Head 5 23 The net result is very stable RF DC levels that are highly insensitive to the operating conditions of the CIS Head Important The RF DC stabilization algorithm Step 2 above remains active as long as no new commands are sent to the CIS Head Once a new command is received stabilization stops and the new command is executed Use the MLO command to turn off the RF DC bias when finished performing measurements and before quitting the program controlling the spectrometer QMF programming example ML28 Activate the mass filter and center its pass band at 28 amu MLA2 52 Activate the mass filter and center its pass band at 42 52 amu MLO Deactivate t
300. ry low reverse gate leakage currents A programmable current source is also applied to the inverting input of the op amp This source serves two purposes it is used to calibrate the gain of the I V converter which changes with temperature and it provides a bias current to the diodes during data collection As a calibrator the current source can output currents from 0 to 5 nA As a bias source it is programmed to provide 500 fA to 64 pA depending on the speed and sensitivity required for a scan High speed scans require high bias currents which reduce the time constant though the diode and high sensitivity scans require low bias currents to reduce the shot noise of the bias current source At 500 fA bias current the Johnson noise current of the 1GQ current source resistor about 4 fAN Hz establishes the noise floor for ion current measurements At higher bias currents the shot noise of the bias current establishes the noise floor For example shot noise associated with a 500 pA bias current is about 12 7 fA VHz In addition the bandwidth of the detector increases with bias current increasing the noise Back to back diodes are used to allow either ion currents Faraday cup case or electron currents electron multiplier case to be measured During calibration procedures the ion current is shunted to ground by a latching relay U701 A latching relay is used so that the relay coil will not be active during either calibrations or measureme
301. ry tightly regulated by a feedback control loop which dynamically adjusts the operating temperature of the filament to keep the total emission current constant The emission of electrons from the filament is limited by space charge CIS Quadrupole Gas Analyzer 3 8 lonizer effects Child s Law limitations The maximum current attainable is a function of the anode to repeller spacing and its potentials The tight design of the filament emission slit region makes it very easy for the filament to emit electrons even under the lowest accelerating fields As a result the SRS CIS is very comfortable operating with 35 eV electrons as required by the CIS 35 mode of operation Ideally the rate of formation of ions should be proportional to the electron emission current In practice the exact dependence between ion signal and electron emission current in small ion sources is complicated by space charge effects and only general trends can be predicted Greater ionization efficiency is to be expected as the electron emission current increases However as the ion density starts to approach the saturation level i e as defined by space charge repulsion effects in the ionization volume the partial pressure sensitivity starts to decrease The linearity range can be extended somewhat by further decreasing the electron emission current to reduce the ion density in the ionizing volume However as the pressure increases the mean free path for the ion molecu
302. s e Contact the factory for instructions on how to return the instrument for authorized service and adjustment CIS Quadrupole Gas Analyzer Chapter 5 Programming the CIS Head This chapter describes how to program the CIS Head from a host computer using the CIS Command Set and an RS232 Link In This Chapter Intro HO 5 3 InrNiwee Bnlnm a 5 3 Intoduction ineo nne suce In bm rM rst iil eme irr fes eM cesar 5 8 Communicating with a Head ocre aeaaeae poanta raana aae eraan esee paa aeae aena eoa aaae aaen aaa ke nasa as 5 3 E Te EMT 5 5 LED IndicCatots 5e iiu ee iu eu uU NL UII 5 5 Command E UC E 5 6 Examples of command Tomate 5 6 Programming tips ir HER Ue pr n ied UR AE I EL Meda due epe ee Oe br dcs 5 7 COMMUNICATION Erres 5 8 Command errors unen ineo edet as RU 5 8 Parameter erEOrs iio tec edd gege 5 8 Jumper Protection violation oes eesecssecssecesecseeceseeeseessneesseeeseeesaecsaecsaecaecaeesseeeseeeeeeeeneeeaes 5 8 Troubleshooting Tools 2 1 irre aasa erue runs nonc maur ance Dan nae D maar aime ua na Ec raa ENEE 5 10 Programming the CIS H ad E 5 11 Initializing the CIS TTT BEE 5 11 Programming the lonizer ecceceeeee cece seen seen eee seen neeeeeen see seen seaeee en seaeeeeeseeeeesaseeneesnseenenenseenenes 5 12 Programming the Detector cccsseccccsseee
303. s Warnings The service information in this chapter is for the use of Qualified Service Personnel To avoid shock do not perform any procedures in this chapter unless you are qualified to do so Read and follow all Safety and Precaution warnings before servicing the product Dangerous voltages capable of causing injury or death are present in this instrument Use extreme caution whenever servicing any of its parts Do not substitute parts or modify the instrument Because of the danger of introducing additional hazards do not install substitute parts or perform any unauthorized modification to the product Do not use the product if it has unauthorized modifications Return the product to SRS for service and repair to ensure that safety features are maintained Use only SRS supplied replacement parts Disconnect the ECU box from the probe before servicing any of the probe components Turn off the emission and wait for at least 30 minutes before removing a probe from a vacuum chamber Serious burns can occur if the probe components are handled too soon Use proper vacuum procedures when handling the probe Avoid contaminating the probe Work in a clean dust free area A clean room compatible environment is best Do not talk or breath on any of the parts Wear gloves Use clean tools during service procedures Wear face masks hair covers and no facial make up Protect the integrity of the Vacuum seals
304. s are controlled by the CPU The set voltages RPL SET and FOC SET are multiplied by 20 and 20 respectively by the bias regulators If the control signal RPL SET is increased the non inverting input and so the output of the op amp U502B will go up increasing the current in the opto isolator s LED increasing Q502 s collector current increasing the magnitude of the negative repeller bias If the control signal FOC SET is increased current is injected via the 61 9kQ resistors R538 and R539 directly into the emitter of Q506 and away from the emitter of Q505 which are biased at ground These currents are mirrored by Q503 504 and Q507 508 to the output node which has a 1MQ resistance to ground via R531 providing an overall gain of 30 Imbalances in currents due to focus plate currents or current mirror mismatches are made up by the op amp U5044 If the output is smaller less negative than it should be the non inverting input to U504A will be positive causing its output to ramp up This increases the current into the emitter of Q506 and decreases the current into Q505 These currents are mirrored to the output increasing the current in Q508 and decreasing the current in Q504 pulling the output more negative The output of U504A will go up by 1V for each IA of ion current collected by the focus plate The output may be digitized by the CPU to monitor the ion current in order to watch for excessive operating pressure Since the focus
305. s as a guide and until physical contact is made between the probe and the ECU s internal connectors 6 Using gentle pressure on the back of the box push the probe s conductors into the ECU s connectors until the front surface of the ECU rests flat against the back of the feedthru flange Warning The alignment of the probe ECU connections is tested at the factory for each individual CIS Analyzer and only slight resistance should be experienced during this step If significant resistance is noted while sliding the ECU onto the probe do not exert excessive force since that might damage the ceramic to metal seals of the CIS Quadrupole Gas Analyzer Installation 1 11 feedthrus Instead rock the ECU box up and down and side to side while gently pushing on its back until the connectors line up Once the connectors are all lined up push the box in the rest of the way Once the ECU is in place use the knobs on the back panel of the ECU box to turn the locking screws and lock the assembly in place Do not overtighten Hand tighten ECU Power Connection Important Do not power up the CIS Analyzer at this time Standard ECU boxes must be connected to the external 24 VDC power supply Insert the 9 pin Type D female cable connector into the ECU connector marked 24 VDC 2 5A on the back panel of the ECU box Units with the optional built in power module Option 02 plug directly into an AC outlet and require no extra power sourc
306. s filter bias sources and 20V for the negative linear voltage regulators The primaries to the inverter are driven by FET s A switching power supply regulator U601 provides 12V square wave drive voltages to the FET s which are sync d to a sub multiple of the master clock Overcurrent protection is provided by U601 on a cycle by cycle basis U601 does not regulate the outputs of the inverter rather its COMP pin is tied high to provide the maximum duty cycle The first of three secondaries is full wave rectified by D611 D614 This output is used only to bias the repeller which allows the filament emission current to be monitored and controlled with high precision The next secondary has a pair of half wave doublers C635 C636 and D615 D618 to provide 250V The third secondary has a full wave rectifier D619 D622 to provide 20VDC which is filtered by C622 C623 and L603 All three secondaries are balanced so that no DC current is drawn in order to avoid saturation in the un gapped transformer core of T601 The positive power supplies 15 for the op amps 12 for the RS232 and MOSFET drivers 33 CLEAN for the signal multiplexers and A D converter and 5 for the logic circuits are derived via linear three terminal regulators U602 605 from the 24V supply The negative supplies 15 for the op amps 12 for the RS232 and 5 for the A D and analog multiplexers are provided by the linear regulators U606 608 from the 20V generated by
307. s highly recommended before operating the CIS Analyzer again Retune the sensitivity of the CIS Analyzer following the instructions in the Tuning chapter before using the unit for any quantitative measurements CIS Quadrupole Gas Analyzer CDEM Handling and Care 7 13 CDEM Handling and Care Continuous Dynode Electron Multipliers CDEM have a history of high performance and dependability in mass spectrometry applications By following the simple recommendations described below the user should achieve a long useful lifetime from these detectors Handling and mounting Handling and mounting of the CDEM should only be performed in a clean vacuum fashion e Work ona clean dust free area Avoid dust lint and any kind of particulate matter e Wear talc free rubber gloves or finger cots e Use properly degreased tools Avoid excessive shock such as from dropping onto a hard surface Remember that CDEM s are made out of glass Operating pressure The recommended operating pressure is 2 10 or less The lower the pressure during any operation the longer the lifetime of the CDEM Never apply voltage to a CDEM at pressures above 10 Torr Operating temperature The safe operating temperature of a CDEM is less than 100 C Bakeout temperature The bakeout temperature must be less than 300 C with no voltage applied across the unit Operating voltage The maximum voltage applied to any CDEM should not exceed 3500V The CIS Analyzer Hi
308. s in the quadrupole is essential to the optimum performance of the mass spectrometer e Do not scratch the surface of the rods e Do not remove excessive amounts of surface material with the abrasives e Use clean tools and procedures Equipment e Clean dust free work area e Latex gloves powder free e One standard OFHC copper gasket for 2 75 CF Flange New and Clean e Replacement bowed e clips SRS Part 0 00579 000 16 count e Phillips head screwdriver P1 head clean e Precision flat head screwdriver 2 5mm head clean e Precision hex head screwdriver 0 050 head e Needle nose pliers e Micro Mesh abrasive sheets 3200 to 12000 grit e Ultrasonic cleaner e Ultrasonic cleaning solution high quality no rinsing residue e 1000mL beaker e Oil free dry nitrogen e Distilled or de ionized water e Petri dish CIS Quadrupole Gas Analyzer Quadrupole filter cleaning 7 21 e Clean oven 180 C setting Procedure 1 Read all warnings at the beginning of this chapter before attempting to service the probe 2 Set up in advance a clean dust free working area where to carry out this procedure 3 Turn off the CIS Analyzer and disconnect the ECU from the probe 4 Wait for the probe to cool down for at least 30 minutes after the emission is turned off Severe burns can result if the probe is handled too soon 5 Without disconnecting the CIS Cover Tee from the vacuum port remove the six bolts from the feedthru flange at
309. s that are routinely pumped down to better than 10 Torr The main use is to check the integrity of the vacuum system and the quality of the vacuum before the wafers are committed to the process Air leaks virtual leaks and many other contaminants at very low levels can ruin wafers and must be detected before the process is started As the semiconductor processes become more sophisticated they also become less tolerant to contaminants Residual gas analysis in a process chamber helps eliminate uncontrollable variables and thus increase up time and production yield and reduce cost of ownership RGA s are not limited to the analysis of gases at pressures below 10 Torr Higher gas pressures can be sampled with the help of a differentially pumped pressure reducing gas inlet system PRGIS consisting of a restriction and a vacuum pump package Common restrictions are pinholes and capillaries which can provide pressure reductions of more than 6 decades of pressure Vacuum pump packages typically consist of a turbomolecular pump backed by a foreline pump The Open lon Source OIS P lt 10 Torr The standard ion source used in most commercially available RGA s is the open ion source OIS This source is considered the do it all source for RGA s It has been around in its cylindrical axially symmetrical version since the early 1950 s A schematic of the OIS design used in the SRS RGA Probe is shown in the following figure Open lon Surce
310. se in the hydrogen partial pressure during this step of the sequence The partial pressure of hydrogen increases by a factor of 100 while the partial pressure of the other gasses barely increase This difference is caused by the low compression ratio that turbo pumps have for light gasses The heavier gasses are being compressed into the dead volume between the turbo pump exit and isolation valve But the turbo pump has insufficient compression ratio to store hydrogen in this manner causing the partial pressure of hydrogen to rise At 2 30 the load lock has been roughed and the turbo pump foreline isolation valve is opened The pressures of H immediately drops back to the base pressure values SRS Residual Gas Analyzer 10 Appendix A At 2 40 the load lock is opened to the main chamber causing a jump in pressure The rise in oxygen and oil pressure indicates that the procedure is operating poorly Even though the load lock was purged three times with 99 999 nitrogen oxygen was still introduced into the chamber This was either caused by a small air leak into the load lock or permeation of oxygen out of the elastomer seals on the load lock The rise in oil partial pressure indicates that the trap on the mechanical pump is exhausted and has allowed oil to backstream into the load lock At 3 09 the valve between the load lock and main chamber is closed and the pressures begins to return towards their base values Oxygen is pumped out of the
311. ses Declaration of Contamination of Vacuum Equipment The repair and or service of vacuum equipment or components can only be carried out if a completed declaration has been submitted SRS reserves the right to refuse acceptance of vacuum equipment submitted for repair or maintenance work where the declaration has been omitted or has not been fully or correctly completed SRS also reserves the right to refuse servicing any vacuum equipment which could potentially be harmful to the personnel carrying out the repair and service of the equipment Contact SRS to request additional copies of this form or if you have any questions regarding the contents of this declaration Description of equipment Equipment type model Serial No Reason for return circle one Repair Maintenance Please describe Equipment condition 1 Has the equipment been used circle one Yes No 2 Describe the operating environment the instrument was exposed to 1 Was any of the equipment exposed to potentially harmful substances circle one No Yes Please attach list of all known harmful substances including chemical name and symbol precautions associated with the substance and first aid measures in the event of accident Were any of the harmful substances Radioactive Yes No Toxic Yes No Corrosive Yes No Explosive Yes No Was equipment decontaminated cleaned before being shipped to SRS Yes
312. settings are changed i e after changing the NF parameter setting or changing detector type This is particularly important if the new settings have not been used in a long time or since the unit was turned on or recalibrated with the CL command e Follow all recommended procedures for the operation of the CDEM Consult the Maintenance chapter of this manual for complete CDEM Care and Handling information Setting up Analog Scans Analog scanning is the most basic data acquisition mode of the CIS Analyzer as a quadrupole mass spectrometer During analog scanning the quadrupole mass spectrometer is stepped at fixed mass increments through a pre specified mass range The ion current is measured after each mass increment step and transmitted to the host computer over RS232 Analog scans are triggered with the SC command The scan parameter can be set for single multiple and continuous scanning operation The mass range for the scan is set in advance with the commands MI Initial Mass and MF Final Mass and the mass increments are fixed with the command SA Scan rate and detection limits are pre programmed by the NF Noise Floor setting A current value is transmitted for MI and after each mass increment through MF for a total of MF MI SA 1 measurements See AP query command For maximum data throughput the ion currents measured are represented as integers in units of 0 1 fA and transmitted directly in Hex format four byte integers with 2 s
313. specting the red LED s on the rear panel of the ECU The Error LED is turned on whenever a hardware problem is detected and it flashes twice if a communications error is generated during programming The Burnt and Leak LED s indicate specific filament problems and are turned on in addition to the Error LED whenever the ionizer s emission is internally shut down or not established as requested 2 Error Queries Querying the Error Bytes with the Error Reporting commands The Error Byte Definitions section of the Programming chapter describes the different error bytes used to store the results of the internal checks The Error Reporting Commands query the error bytes and can be used to quickly diagnose problems RGA Windows supports all the Error Reporting commands and constantly monitors the value of the Error Bytes Error Report windows immediately announce all detected errors and identify the different problems based on unique Error Codes Refer to the next section of this chapter for Troubleshooting information specific to each Error Code Users developing their own control software should integrate the Error Reporting commandis into their software and use them periodically Consult Error Checking the CIS Analyzer in the Programming chapter of this manual for details Use the Error Byte Definitions listing to obtain the Error Codes for the detected errors Error Checking Tips e Keep an eye on all three red i e error reporting
314. ss filter requires two potentials be applied to two pairs of rods The potentials are given by Vx y t U Vocos ot where U is a DC potential amplitude and V is an RF potential amplitude The physics of the quadrupole mass filter show that the resolution of the instrument improves with the frequency amp 2zf the ions interact with the RF field for more cycles however the required RF amplitude increases with the square of the frequency An operating frequency f22 7648 MHz requires an RF amplitude Vo of 1284 V 2568 Vpp to measure ions with mass of 300 amu 8 56 Vpp amu The ratio of DC to RF amplitude U Vo controls the fractional mass resolution M AM For f 2 7648 MHz the DC potential U will 215VDC on one rod pair and 215 VDC on the other for masses of 300 amu The rod structures are primarily capacitive so to reduce the circuit drive requirements the rod reactance is resonated with an inductance The advantages of this resonant drive circuit is the primary reason for operation at a fixed frequency Ions with the selected mass are collected in a Faraday cup The ion currents can be very low a few femtoamps and have a very large dynamic range up to about 100 nA A log I V converter capable of simultaneously measuring ion signals over several orders of magnitude is a natural choice Low Pass filtering of the signal is essential in the presence of the large rod potentials To improve the detection limit by overco
315. stant would be over 40 hours This emphasizes the importance of leak test ports on vacuum hardware In such situation it is common to place a bag over the body of the valve and fill the bag with helium The RGA allows us to consider using gases other than helium The permeability of helium through elastomeric seals can give a false leak reading And as in manifolds unless the helium can be strictly confined to the valve body it may spread to adjacent connections Given the amount of work and lost time required to remove and repair large valves false leak readings are expensive A second test with another gas such as argon can confirm that a suspect valve is leaking before starting out on the repair SRS Residual Gas Analyzer 14 Appendix A Conclusion An RGA is a real eye opener for users of vacuum systems With an RGA the process of working with vacuum systems is elevated from an empirical trial and error approach to a systematic approach The status of the vacuum system can be constantly assessed When an experiment or process is having problems the possibility of contamination or leaks in the vacuum system can be immediately ascertained The RGA provides not only troubleshooting but also historical data Slow trends in a vacuum system can be noticed and acted on before they become serious problems Hard to correlate cause effect relations are much easier to establish with the wealth of statistical data that can be obtained with a daily sp
316. sure Sensitivity Factors uueeesseeeeeeeese eese nennen nennen nnnm rnnt nnns 2 15 Chapter 3 Quadrupole Probe 3 1 Iottrogd ett 3 2 nr 3 3 DO SCKIPtlON Ee EU 3 3 Principle of operation eeeeeeeeeeieee esee enne eeee enne nennen nana nnne mnnn nnnm nnmnnn nnmnnn nnmnnn ennnen 3 4 Parameter iu f 3 6 Quadrupole mass UE 3 9 NET de le Vu C 3 9 Principle of operation 5 hone ee bur diee eu 3 10 Mass Range Resolution and Throughput eese 3 12 Zero Blast Suppression eseu Neue ediderit ILI Eed 3 14 lon Detector idu ea duced dence cedere eec eae eee eg 3 15 Neid e LEE 3 15 Faraday Cup operation eeseesesieeseseeeeeeeeeeeen einn nn nnne anete a re napaa Onera aas Tannin aphan tn Rusa as 3 16 Electron Multiplier Operation 1eeeeeeeeeeiees sienne nennen nennen nnne nennen nn nnn na snnm a nnn n nnns 3 16 Upgrading to an Electron Multiplier Detector eene 3 19 Pumping System Requirements eesieessieeseeeeeeees esee nennen nennt nina natnm n se tn insana assis san anneanne 3 21 Pump ODptlOriS 1 eege eege Eeer 3 21 Chapter 4 Electronics Control Unit 4 1 uidere Freie Elbe eccL D 4 2 Front G
317. surements Please consult the Tuning Commands List in the Programming chapter of this manual for details on the DS and DI commands Note The sensitivity of the peak widths to the DC TWEEK voltage can accurately be approximated to 1 amu per 550mV 28 bits In other words a 550 mV increase in DC Tweek voltage causes a 1 amu decrease in the width of any peak The DC Tweek voltages span from 2 5 to 42 5 V with increments of 19 6 mV per bit 255 total bits This corresponds to a peak width adjustment range of 4 5 amu and minimum increments of 0 036 amu per bit As described above the peak width tuning procedure requires the introduction of two known gases into the vacuum system A low mass gas 1 20 amu recommended is used to adjust peak widths at the low end of the mass scale a high mass gas with a mass to charge ratio close to the upper limit of the scanning range of the CIS Analyzer is used to adjust the widths at the high end of the mass scale Several analog scans are performed on the sample and the values of DI nominally 128 and DS nominally 0 are adjusted until all peaks show the correct target width CIS Quadrupole Gas Analyzer Peak Tuning Procedure 6 9 The formulae used to correct the calibration parameters during peak position adjustment are described next Low Mass Peak Width Adjustment To increase the low mass peak width by an amount Am amus modify the value of DI from its original value Dia to DI DI Am 2
318. system is suitable At atmospheric and higher pressures a two stage reduction based on a capillary and aperture is used These two systems will be used to illustrate the design of pressure reduction systems for RGA s Vacuum Process Sampling 10 to 10 5 mbar Figure 1 shows a schematic of a basic pressure reduction system The system has two paths to the RGA a high conductance path and an aperture path The high conductance path through Valve Hi C is provided so that the RGA can monitor the ultimate vacuum of systems before a process begins The Hi C path is also used when leak testing the vacuum system with the RGA Software s leak test mode The aperture path provides the pressure reduction for when the vacuum process is operating at pressures up to 10 mbar The design of the aperture path is straightforward First the RGA operating pressure is chosen for example 10 mbar The pressure P and the pumping speed S determine the throughput of the aperture Q by the equation Q P S To keep the system cost low a small turbo pump is chosen For a 70 liter s pump the required throughput is 7 x 10 mbar liter s The throughput of the aperture is related to its conductivity C and the pressure drop AP by the equation Q C AP The process pressure determines the pressure drop thereby determining the required conductivity Formulas for conductivity of various geometries e g capillaries and pinholes are available in many references
319. t The most common reason for this error is overpressure caused by a serious leak in the vacuum system or high a pressure gt 10 Torr in the process chamber In the event of an overpressure detection the filament emission and the electron multiplier are immediately turned off and the Error and Leak LED s are turned on to indicate the problem The Leak LED will also be turned on if the filament is excessively worn down or damaged The following troubleshooting steps are recommended Important Try turning the filament on after each step below The CIS Head must be connected to a process chamber and operated at pressures under 10 Torr for the instrument to operate correctly CIS Quadrupole Gas Analyzer Error Code Type of Error Error Message Error Cause Troubleshooting Error Code Type of Error Error Message Error Cause Troubleshooting Basic Troubleshooting 8 7 Check the pressure in the vacuum system Check for leaks open valves or large sources of contamination that might be causing severe overpressures If the pressure is OK i e 10 Torr in the ionizer 10 Torr in the quadrupole volume check for shorts in the ionizer assembly Using an ohmmeter check the conductance between the ionizer s connectors and the vacuum system The ionizer feedthrus can be easily identified using the drawings in the Probe Assembly Chapter If a short is detected remove the probe from the vacuum system inspect
320. t is achieved FL The command is excecuted using the default parameter value Default 0 05 mA FL Returns over RS232 the value of Electron Emission Current in mA actually flowing through the ionizer Important The number returned by the query command will always be very close but rarely identical to the current value set with the FL param command CIS Quadrupole Gas Analyzer 5 32 lonizer Control Commands The difference observed will never exceed 0 02 mA The value returned is the actual electron current circulating through the ionizer as internally calculated by the CIS head The discrepancy is due to the finite resolution of the digital to analog converters used to program the ionizer s emission current Error Checking The absence of a parameter i e FL is treated as a bad parameter error The STATUS byte is echoed to the host computer at the end of the command excecution and it should be checked to determine whether the requested electron emission current was succesfully established If Bit 1 of STATUS is found set FIL ERR should be immediately checked to identify the specific problem See EF command in the Error Reporting Commands list It is good practice to attempt the command a second time before declaring a hardware problem Once it has been set FIL ERR can only be cleared after succesfully turning on the filament IEparam param 0 1 Description Ion Energy eV Echo STATUS error byte or q
321. t the optimum performance of the instrument is not compromised during the installation process Pressure Reducing Gas Inlet System For applications that involve sampling gas pressures gt 2mTorr a Pressure Reducing Gas Inlet System placed between the gas chamber and the CIS ionizer might be required to complete the installation of the CIS Analyzer Consult the High Pressure Sampling section in the General Operation chapter of this manual for more information on this subject The Pressure Reducing Gas Inlet System must be available before the installation process can begin Pressure Reducing Gas Inlet systems for several different pressure ranges can be ordered directly from Stanford Research Systems or from your authorized local representative Unpack and or check the integrity of the Gas Inlet System components before the installation process starts Also read the installation instructions at this time to make sure all the necessary hardware required by the manufacturer is available If everything is present and in order install the Gas Inlet System carefully following the manufacturer s CIS Quadrupole Gas Analyzer Installation 1 5 instructions As a double check remember that once the inlet system is installed it must have a 2 75 CF flange available to attach the CIS Probe Warning Verify that the vacuum port is electrically grounded before attempting the installation of the Gas Inlet Valve on the vacuum chamber Probe Instal
322. tally opened and the process chamber is pressurized The Background Filament Protection mode immediately detects the problem and turns off the filament The change is easily detected because the Filament LED turns off and the Error and Leak LED s simultaneously turn on A visual inspection of the red LED s is all that is needed in this case to detect and diagnose the problem however a computer could do the same diagnosis with the help of the query commands The ER command used to monitor the STATUS byte regularly returns a non zero byte value Further analysis shows that bit 1 is set indicating a filament problem The EF command is then used to read in the value of FIL ERR Bit 6 is found set indicating that the filament was unable to set the requested emission current and had to be shut down CIS Quadrupole Gas Analyzer 5 26 Programming the CIS Head Error Code FL6 The problem is quickly diagnosed as an overpressure using the Troubleshooting chapter directions The error is also immediately reported by the RGA Windows software as Error Code FL6 and the Troubleshooting section can be consulted to solve the problem Example 3 The CIS Analyzer is turned on and after all the internal checks are performed the green Power LED and the Error LED are turned on The red LED signals the operator that a problem was detected A 24V P S error is not expected since the Power LED is on The ER command returns a STATUS byte with bit 4 s
323. te stesse tanen setas satanas saa as 2 8 CIS Mode 10 lt P lt 10 TOIT io ie cae odeur ttt nl raat dae t tuu tese Ud Leur bate 2 9 High Pressure Sampling P gt 1 mTorr cessisse esses eeen eene enne innen nnn nennt nnn nn asina nnn n nnn nnns 2 11 Partial Pressure Analysis Basics 4 eeeeeeeeeeeeeeeeeeee eee enean nnn saint h innen nnmnnn nnmnnn nnns 2 12 How Mass Spectra are Interpreted aeseeeeeeeeeseesseeseeeeeee enne nnnm nent nnns 2 12 Partial Pressure Measurement e eeeeeeeeeeeeeeeeee enne nennen nhan nnn nn nnmnnn nnmnnn nnna 2 13 Partial Pressure Sensitivity Factors ueesesseeeeeeeeeseeeees nennen nnne n nennt annnm n nennt nnns 2 15 CIS Quadrupole Gas Analyzer 2 2 The SRS Closed lon Source Quadrupole Gas Analyzer The SRS Closed lon Source Quadrupole Gas Analyzer The Closed Ion Source CIS Quadrupole Gas Analyzer manufactured by Stanford Research Systems is a differentially pumped quadrupole mass spectrometer specifically designed for the direct measurement of minute trace gas impurities in process gases at pressures below 10 Torr In its most simple configuration an SRS CIS Analyzer consists of a CIS probe and an Electronics Control Unit ECU The basic setup is shown in Figure 1 CIS Mounting Flange CIS Cover Tee To CIS lonizer b Pumping System Port
324. ted perform a filament and or ionizer replacement following the procedures described earlier in this chapter Inspect the CDEM for signs of arcing and contamination A blue tinge is an indication of an electrical arc while brown indicates contamination A burned black color may indicate both arcing and contamination have occurred If excessive contamination is evident take the necessary steps to identify and reduce contamination sources in the vacuum system 9 CDEM Removal Note the position of all parts and their orientation before disassembly The CDEM consists of a straight four channel tube made out of glass with a cone of the same material attached to the front end It is held upright next to the FC and away from the axis of the analyzer by a clamp and a clip The clamp wraps around the multiplier tube and is connected to a neighboring rod It assures proper alignment of the cone and provides the electrical connection to the High Voltage power supply A hole on the side of the FC Shield allows space for mounting the CIS Quadrupole Gas Analyzer 10 11 12 13 14 15 16 17 CDEM Replacement 7 19 cone very close to the FC top The clip is spot welded to the side of the FC shield and holds the lower end of the multiplier s tube at ground Chrome electrical coatings deposited at both ends of the multiplier provide the necessary electrical contacts A plate CDEM Anode mounted at the exit of the CDEM collec
325. ter at the end of the scan Please see HP Command The current value needs to be accounted for but it does not need to be stored or displayed e The measurements are performed with the detector that is active at the time the scan is triggered Parameters HS Continuous scanning mode The CIS Analyzer produces a continuous string of histogram scans A new command must be sent to the CIS Head in order to stop the scanning activity Once the command is received the scan is immediately stopped all transmission is halted and the transmit buffer is flushed all remaining data is lost The command which stopped the scan is executed right after the buffer is flushed HS0 Do nothing command Commonly used to interrupt continuous scanning mode HSparam param 1 255 Multiple scans The number of scans specified by the parameter is executed Scanning is immediately stopped when a new command is received as in the case of continuous scanning HS The default parameter value is used for multiple scan excecution Default parameter value 1 single scan Error checking Number parameters must be within the specified range and be integers No query format is allowed Programming Tips e Any command received by the CIS Head while scanning will immediately stop the data acquisition and clear the transmit buffer Remember to also clear the computer s receive buffer to reset the communications The command which stopped the scan is executed r
326. tgassing The OIS is a hot cathode ion source The filament wire i e the cathode must be heated to high temperatures 1 e 1300 C in order to establish an electron emission current In the high vacuum most of the energy required to heat the filament is dissipated to the surroundings through radiative processes As a result the entire ionizer and the adjacent walls run hot The elevated temperatures result in increased outgassing from the OIS itself and from the adjacent chamber walls In the most benign cases outgassing simply modifies the composition of the gas mixture being measured However under some circumstances outgassing can be a serious problem and even ruin experiments and samples The gases emitted by the outgassing process obscure the minimum detectable partial pressures MDPP s of many important gases including H2 H20 N CO and CO Degassing the ionizer can help minimize some of the background signals however this is usually only a temporary solution During a degas the ion source is ramped up to a temperature significantly above its normal operating value and bombarded with high energy electrons in order to accelerate the outgassing process Some RGA manufacturers offer UHV versions of their OIS with anodes and sometimes entire ionizer assemblies made out of platinum clad molybdenum wire This highly inert material exhibits decreased adsorption for many gases and provides reduced outgassing and ESD Water
327. the CDEM Clamp hole and the top groove should be correctly lined up with the edge of the alumina spacer s alignment hole Install new bowed e clips in all the grooves located above the alignment holes of the bottom alumina spacer The clips hold the filter tightly against the exit plate Finally install the filament and the repeller plate following the necessary steps from the Filament Replacement section in this chapter Visually inspect the probe to make sure all the parts are in place and correctly aligned Use an ohmmeter to make sure the electrodes are electrically isolated from each other and from the body of the flange ground Once satisfied install the probe back in the vacuum system and perform a complete Probe Bakeout before using the instrument for measurements Perform a peak tuning procedure on the unit CIS Quadrupole Gas Analyzer 7 24 SRS Probe Refurbishing Service SRS Probe Refurbishing Service The procedures described in this chapter are designed to guide the user through the various steps needed to maintain and or repair the different components of the CIS probe These procedures should only be carried out by qualified personnel who fully understand the critical alignment aspects of the instrument Users who do not feel comfortable or simply do not have the time to go through the different maintenance steps can choose to send the unit back to the factory for a complete Probe Refurbishing Service Please contact SR
328. the instrument is used deposits form on the ionizer parts and on the filter components The performance of the spectrometer is affected by the build up of electrostatic charge on the contaminated surfaces The symptoms of the problem are decreased sensitivity decreased resolution and in severe cases unusual peak shapes A periodic bakeout helps keep the quadrupole probe clean and minimizes this problem Warnings To avoid fire risk use a good quality heater with a built in temperature limit switch High performance custom designed heating jackets can be ordered from a number of manufacturers Consult SRS or your local representative for details To avoid overheating the components use a reliable temperature controller to regulate the bakeout temperature Donotleave the system unattended for long periods of time To avoid damage to the electronic components detach the ECU from the probe during bakeout Do not operate the instrument during bakeouts To avoid burns cover the heater with heavy insulation during bakeout and do not touch the probe until it cools down after bakeout is over Use only metal gasket seals during bakeout since rubber gaskets might melt CIS Quadrupole Gas Analyzer 7 6 Probe Bakeout Procedure 1 The quadrupole probe must be mounted on the vacuum system and at base pressure Note If necessary use an isolation valve to separate the CIS Analyzer from the vacuum process chamber during routi
329. the main inverter Schematic name QMSE V1 Signal Conditioning The output from the mass filter is a very small ion current which is proportional to the pressure of the selected mass The lowest pressure which may be measured by the instrument is proportional to the lowest current which may be detected Extreme care is required to achieve low drift and low noise current measurements at these very low CIS Quadrupole Gas Analyzer Description of Schematics 9 15 current levels In addition the instrument needs to measure a wide range of pressures which requires current measurements over a wide range The sensitivity of the ionizer and mass filter is about 100uA Torr and is nearly constant from 0 to 5x10 Torr so we expect ion currents from 0 to 5 nA To accommodate this large dynamic range a log I V converter is used whose output is amplified filtered and digitized by a 16 bit A D converter The high resolution A D is required to assure that the quantization noise of the A D is smaller than the shot noise of the I V converter s bias source and to provide sufficient resolution At the core of the detection system is the log I V converter A standard arrangement is used where the current is applied to the inverting input of a very low bias current op amp U700 and a diode is used between the output and the inverting input of the op amp Small signal JFETs transistors Q700 701 are used as diodes as they have well characterized and ve
330. the meter without any gain switching being necessary The microprocessor automatically configures the electrometer and connects its input to the correct signal based on the type of detector being used The electrometer is completely autoranging and measures both positive and negative currents with the same accuracy and resolution Its operating range covers current magnitudes between 1 32 10 and 10 A The accuracy of the measurements is insured by an internal calibration procedure that calibrates the output of the electrometer against input current over its entire operating range and stores a calibration table in the non volatile memory of the CIS Head Instead of simply relying on the intrinsic logarithmic I V behavior of the electrometer a digital logarithmic interpolation algorithm calculates the currents from the calibration curve The I V response of the electrometer can be recalibrated at any time through a single command CL supported by the RGA Windows software Calibrate Detector option in the Head menu making it possible to generate accurate readings under different operating conditions Excellent resolution is achieved using a 16 bit A D converter to digitize the output of the electrometer The bandwidth and detection limit of the logarithmic electrometer are fully programmable This programmability is achieved biasing the electrometer with extra current from a microprocessor controlled current source The biasing current is added
331. the test gas the partial pressure will rise The response is immediate if the leak is in a direct path from the outside to the inside of the system Figure 6 contains the result of a leak test with helium on a vacuum chamber The tester moves the helium probe towards and then past the leak causing the first peak Once the location of the leak is bounded the tester tries to precisely locate the leak For most situations leak testing is straightforward and no different than traditional methods In the following sections we discuss a few situations where traditional methods fail and how the RGA provides a better method SRS Residual Gas Analyzer 12 Appendix A Chamber Leak Test Hali um Tor Pie EE KKK KS SE al a ae ae o neoa IP a ERI PE Dro rr OOOO OHO 44 rer Time Hh mm s Figure 6 Helium Leak Test Data The partial pressure of the test gas is directly related to the leak rate into the chamber Assuming that the vacuum pump is not operating near its compression limit the throughput of the test gas is equal to the product of the partial pressure and the effective speed of the pump at the RGA ionizer Q S P In Figure 5 the partial pressure was measured in Torr The effective speed of the turbo pump for helium was approximately 50 liter s The largest peak in this data at 4 x 10 Torr represents a leak of 1 5 x 10 scc sec 0 76 scc sec 1 Torr liter s From this figure we can estimate a minimum detectable leak of
332. the vacuum system so that the probe can be reassembled in the exact same way at the end of the procedure Mark the side of the flanges with a permanent marker if necessary The ionizer the filter CIS Quadrupole Gas Analyzer 7 8 lonizer Replacement and the detector are now fully exposed and easily accessible The alumina seal SRS 7 00787 remains attached to the CIS Port held in place by a retaining ring Make sure the crescent washer SRS Part 0 778 is still attached to the anode tube Otherwise use long pliers or a long wire to remove the washer from the inside of the CIS Cover Tee CIS Mounting Flange Feedthru Flange Process Chamber CIS Cover Tee Vacuum a lonizer Probe Assembly enn Pumping System 2225775555 Figure I Probe Removal for Ionizer Replacement 7 Carry the probe to a clean dust free area immediately Avoid contamination using handling procedures compatible with high vacuum requirements 8 Hold the probe in a upright position and do a thorough visual inspection of the unit Check for loose damaged misaligned and contaminated components This is the best time to fix any problems that might be detected 9 Using the clean flat head screwdriver disconnect the repeller plate from its filament post fully exposing the filament and the anode slit Be careful not to damage the delicate filament if you plan to use it again 1
333. they are executed Since the command execution time can be rather long the CIS Head prompts the end of execution by sending back the value of the STATUS byte to the computer Always check the value of the STATUS Byte returned for possible errors In cases where a hardware error is reported retry the command one more time before declaring a hardware problem With the exception of the ion current values the data tramsmitted by the CIS Analyzer consist of ASCII character strings terminated by a lt LF gt lt CR gt terminator Ion signals are represented as integers in units of OTT Amps and transmitted directly in hex format four byte integers 2 s complement format Least Significant Byte first for maximum data throughput CIS Quadrupole Gas Analyzer 5 8 Communication Errors Communication Errors Communication errors are signaled to the user flashing the Error LED a couple of times setting Bit 0 of the STATUS error byte and setting the error specific bits of the RS232 ERR error byte Many different circumstances can result in a communication error being reported after a command string is received by the CIS Head Some problems are detected early by the command handler and result in the command never being executed Other errors are found later during the actual command execution and they result in the execution being immediately halted The following is a list of the communication errors that might be encountered during the analys
334. tings An offset correction factor is calculated and stored in memory that it is then automatically used by the Miniscan procedure to correct all ion currents measured The CA command will also update the internal scan parameters to assure that the CIS Quadrupole Gas Analyzer 5 20 Programming the CIS Head correct RF levels i e as specified by the last Peak Tuning procedure are programmed on the RF rods as a function of mass during the Miniscan Single Mass Measurement example The following list of commands can be used to perform a single mass measurement at 28 amu First the electron multiplier is turned off and the FC is connected to the electrometer the noise floor is set to the maximum averaging best signal to noise ratio and longest measurement time the zero of the detector is readjusted and the measurement is triggered The single current value returned by this command is the maximum current in the 28 0 3 amu region of the mass spectrum and must be corrected with a sensitivity factor to obtain the actual partial pressure reading at mass 28 Important The RF DC on the QMF are left at 28 3 amu at the end of this measurement and the MRO command can be used to turn them off Important The CA command turns off the RF DC at the end of its execution HVO High Voltage CDEM 0 Volts FC detection enabled NFO Maximum averaging slowest scan rate selected CA Readjust the zero of the detector for clean baseline and update th
335. tio This convenient way of speaking is strictly valid for singly charged ions only The CIS Analyzer as a Mass spectrometer The CIS Analyzer can perform both analog and histogram scans over its entire mass range Partial pressure gas analysis relies on the interpretation of the spectral data generated by these two data acquisition modes to completely characterize both qualitatively and quantitatively a vacuum environment RGA Windows uses the two modes to generate the data for the Analog and Histogram Scan Modes Analog scanning is the most basic operation of the CIS Analyzer as a quadrupole mass spectrometer During analog scanning the quadrupole mass spectrometer is stepped at fixed mass increments through a pre specified mass range The ion current is measured after each mass increment step and transmitted to the host computer over RS232 Analog scanning allows the detection of fractional masses and provides the only direct view of the peak shapes and resolution of the instrument CIS Quadrupole Gas Analyzer Basic Data Acquisition Modes 2 7 A Histogram Bar Mode Scan consists of a succession of individual peak height measurements over a pre specified mass range A single value is used to represent the peak heights at each integer mass within the range The peak height measurements are made with the Peak locking scanning procedure described in the next section Histogram scanning is one of the most commonly used modes of operation
336. tion of the CIS Analyzer to the ultimate theoretical limit of the mass filter See the Quadrupole Mass Filter section in the Quadrupole Probe chapter of this manual for details on that limit Temperature effects on the mass scale calibration As the temperature of the CIS Head changes two different effects affect the calibration of the mass scale CIS Quadrupole Gas Analyzer 6 10 Peak Tuning Procedure e Small temperature changes Drift in the voltage output of the RF Driver that controls the RF power supply can cause the mass peaks to shift their position in the mass spectrum In order to correct against this effect the RF driver output is checked at the beginning of each analog and histogram scan at 0 and 128 amu The internal calibration parameters used by the firmware to step the RF during scans are updated so that the control levels specified by the RI 0 amu and RS 128 amu parameter values are correctly set at the present temperature e Large temperature changes The sensitivity of the RF power supply to its controlling voltages might be affected or more fundamentally the relationship between mass and RF levels in the filter might change for example if the QMF changes its physical dimensions In this case a Peak Tuning procedure will be necessary to reestablish the mass axis scale CIS Quadrupole Gas Analyzer Sensitivity Tuning Procedure 6 11 Sensitivity Tuning Procedure All quantitative calculations performed with th
337. to be combined The low ultimate vacuum of contemporary diaphragm pumps makes them suitable as a foreline pump The combination of these modern technologies means that an atmospheric sampling system can be constructed into a very small packages less than 8 inch high in a 19 inch rack mount chassis which is portable and easy to operate Conclusion Although the RGA is intrinsically a vacuum instrument inlet systems are easily designed that allow it to sample gasses at any pressure more descriptive name for such systems would be online quadrupole mass spectrometer Mass spectrometry is a well proven analytical technique but traditionally used an expensive large machine Reduction in cost of quadrupoles and vacuum pumps along with the development of easy to use software interfaces makes process analysis with mass spectrometry an attractive technique Further Reading Lewin O An Elementary Introduction to Vacuum Technique American Vacuum Society New York 1987 Moore J H Davis C C and Coplan M A Building Scientific Apparatus 2nd ed Addison Wesley New York 1989 SRS Residual Gas Analyzer Appendix C SRS RGA Output Control Options O100TR and O100TS WARNINGS Please note that the TTL output signals are always active high and may not be configured otherwise This means that any time an output channel s alarm is triggered its corresponding TTL signal is set to a high TTL level The untriggered state is a Low TT
338. tor settings at the time the scan is triggered e The ion detector can be zeroed prior to the measurements performing an analog or histogram scan or using the CA command under the same detector settings An offset correction factor is calculated and stored in memory that it is then automatically used by the Miniscan procedure to correct all ion currents measured The CA command will also update the internal scan parameters to assure that the correct RF levels i e as specified by the last Peak Tuning procedure are programmed on the RF rods as a function of mass during the Miniscan Parameters MRO The RF DC voltages are completely shut down and no measurement is performed no ion current is transmitted back to the host computer Use this command format at the end of a set of single mass measurements to make sure the RF DC are completely turned off MRparam param 1 M MAX A Miniscan is performed around the mass number selected by the parameter and the maximum ion current is sent out over RS232 The upper mass limit depends on the SRS CIS model number M_MAX 100 for CIS100 200 for CIS200 and 300 for the CIS300 CIS Quadrupole Gas Analyzer 5 46 Scan and Measurement Commands Error Checking The command does not accept query or default parameters Programming tips e Single mass measurements are commonly performed in sets where several different masses are monitored sequencially and in a merry go round fashion For b
339. tput 2 5V and times 1 increases the rods DC EMIT SET This output times 1 or 1OmA V sets the emission current RPL SET This output times 20 sets the repeller and filament bias FOC SET This output times 30 sets the focus plate bias HV SET This output times 500 sets the electron multiplier bias OFFSET This output 2 5 amp times 001 fixes the detector offset LJ L P ra CH CIS Quadrupole Gas Analyzer 9 10 Description of Schematics 5 OFFSET This output 2 5 amp times 001 fixes the reference offset 6 CAL This output 2 5V then times 2 is the calibration source RF Amplitude Detection The amplitude of the RF is detected by a full wave charge pump detector In order to provide a symmetrical load to the generator the amplitude on both rods is detected and summed The charge pump works as follows as the potential on the rod reaches a peak the 0 5 pF capacitor C750 on the PCB which holds the flange socket is charged to the maximum voltage Vp Vdc Vdiode with current flowing to ground via D303 a Schottky diode During the next half cycle C750 is charged to Vp VDC Vdiode with current flowing through D302 from the virtual ground at the inverting input of U305 The total charge transfer to the op amp is C x dV C x Vpp 2Vdiode This charge is pumped every cycle from two charge pumps so the current is I 2fC Vpp 2V diode For C20 5pF and f 2 7648 MHz and ignoring Vdiode the current is 2 76uA Vpp T
340. tra Analog and Histogram Echo Query Response Set the Initial Mass value in amu for Analog and Histogram scans The first ion current transmitted during an analog or histogram scan corresponds the mass to charge ratio specified by the MI parameter Note that the initial mass setting is shared by both Histogram and Analog scans and must be an integer number Parameters MIparam param 1 M MAX The parameter represents the initial scan mass in amu units The upper mass limit depends on the SRS CIS model number M_MAX 100 for CIS100 200 for CIS200 and 300 for the CIS300 MI The initial mass value is set to its default value Default value 1 MI Returns the value of initial mass to be measured during scans Error checking Number parameters must be within the specified range and be integers The mass value set by MI must always be less than or equal to the final mass setting MF or else a parameter conflict communications error is generated The absence of a param i e MI generates a bad parameter error MRparam param 0 M MAX Description Single Mass Measurement Echo Ion Current Excecute a single ion current measurement at the specified mass setting The parameter is the integer mass number mass to charge ratio in amu units at which the measurement is performed The type of detector and noise floor settings to be used by the measurement must be selected in advance with the NF and HV commands CIS Quadrup
341. ts the secondary electrons The whole assembly is self aligning CDEM Clip Remove this screw only Faraday Cup Shield CDEM Clamp Figure 4 CDEM Replacement Using the clean flat head screwdriver remove the small screw that fastens the clamp to the HV rod and rotate the entire multiplier about its axis until the clamp s end points away from the FC Shield Holding on to the clamp s end pull the multiplier out of the clip Unpack the new multiplier Notice that the multiplier has a mounting clamp already in place so there is no need to keep the old one Avoid contamination Install the new multiplier in place reversing the removal steps Clip it in place rotate it about its axis so the clamp fits into the slot in the HV rod and fasten the clamp with a small screw Visually inspect the assembly and do any adjustments that might be necessary The CDEM should be standing straight up centered between its two neighboring rods and with its cone facing straight into the FC shield s hole The CDEM anode should be 1 2 mm away from the multiplier s exit and it can easily be pushed up or down with pliers for correct placement There should be no electrical contact between the cone HV and any part of the probe If necessary loosen the clamp s screws to do adjustments Once satisfied with the alignment mount the probe back on the vacuum system and pump it down Check the correct rotational orientation of the feedtrhu flange i e sam
342. ts the status of the CDEM bias at all times Since it takes time for the CDEM and for the electrometer to settle completion of the command is prompted to the host computer transmitting the STATUS byte value over RS232 Important e Faraday Cup detection is the default detector setting upon a power on reset of the CIS head e The voltage set by this command is the output of the high voltage power supply A IMOhm resistor is placed between that output and the CDEM s cone CDEM s typically have an internal resistance in the order of 100 2500 MOhm and consequently the voltage measured on the CDEM will always have a magnitude smaller than the value returned by a HV command i e the CDEM becomes part of a voltage divider in conjunction with the 1MOhm resistor e Itis good practice to readjust the Zero of the ion detector every time the type of detector FC or CDEM is changed This is particularly important if the new detector settings have not been used in a long time or since the unit was CIS Quadrupole Gas Analyzer Detection Control Commands 5 37 turned on or recalibrated with the CL command See the CA command for details and more recommendations Parameters HV 0 Use this parameter value to turn off the Electron Multiplier and enable Faraday Cup FC Detection The following steps are taken e The biasing voltage of the CDEM is set to Zero i e no ion collection and no gain e The electrometer is connected to the
343. uble purpose of drawing the ions away from the ionization volume and keeping the ionizing electrons away from the quadrupole mass filter Electron leakage into the filter is only detectable at low mass settings 1 to 10 amu and can easily be eliminated biasing the extraction plate more negative than the repeller plate Careful adjustment of the voltage results in optimum coupling of the ion beam into the QMF and maximum sensitivity If the filament is emitting electrons at the time the command is invoked the extraction voltage is immediately reprogrammed while the ion energy electron energy and electron emission currents remain unaffected If the filament is off the new extraction voltage value is stored in memory for the next time the filament s emission is activated Command excecution times vary depending on the pre existing ionizer conditions The end of the command excecution is prompted to the host computer sending out the STATUS byte over RS232 Parameters VFparam param 0 150 The parameter represents the magnitude of the extraction plate bias potential in Volts The actual bias voltage is negative The STATUS byte is transmitted at the end of command execution VF The default extraction plate biasing voltage value is used to excecute the command Default 40 V VF Query the extraction plate biasing voltage setting Error checking Number parameters must be integers within the accepted range The absence of a para
344. uery response Set the Ion Energy to one of two possible levels Low 4eV or High 8eV The parameter represents the ion energy level 0 for Low and 1 for High Since the axis of the quadrupole mass filter is at ground the ion energy in eV is equal to the anode tube s bias voltage in Volts Important The anode tube is always biased regardless of the filament s emission status Upon reset the anode bias level is set to the default value Parameters IEO Low ion energy 4 eV IE1 High ion energy 8 eV IE The default Ion Energy parameter value is used to run the command Default 1 gt high ion energy 8 eV IE Query The value of the ion energy parameter is returned over RS232 in ASCII format Note that it is the parameter value and not the actual voltage level that is returned Error checking Number parameters can be 0 or 1 only and must be integers The absence of a parameter i e IE is treated as a bad parameter error CIS Quadrupole Gas Analyzer lonizer Control Commands 5 33 VFparam param 0 150 Description Extraction plate voltage Volts Echo STATUS Error Byte and query response Set the extraction plate voltage in the ionizer The parameter represents the magnitude of the biasing voltage negative in units of volts The ions formed inside the anode tube are extracted into the quadrupole mass filter by the negative attractive potential of the Extraction Plate The plate serves the do
345. upole Mass Filter RF P S STATUS Bit affected 4 Error Byte affected QMF_ERR Error Reporting Command EQ Error Codes prefix RF Power on check Yes The RF power supply that biases the rods of the Quadrupole Mass Filter is thoroughly checked upon a power on reset and can be tested at any time using the query command EQ The RF amplitude is set at the level corresponding to the maximum mass value for the head 100 amu for CIS100 200 amu for CIS200 and 300 amu for CIS300 and the following tests are done e The voltage on the primary of the RF transformer is checked to make sure it is at least 2V lower than the DC voltage used to power the instrument e The amount of current flowing through the primary of the transformer is checked to make sure it is less than 2 0 Amps e RF PRI is also checked against RF SET to make sure the driver is not in current limiting mode CIS Quadrupole Gas Analyzer 8 12 Built in Hardware Checks If a problem is detected in any of these checks Bit 4 of STATUS is set OMF ERR is updated and the Error LED is turned on Filament s Background Protection mode STATUS Bit affected 1 Error Byte affected FIL_ERR Error Reporting Command EF Error Codes prefix FL Power on check No The filament is by far the most carefully protected component of the CIS Analyzer When electron emission current is requested the CIS Head biases the ionizer and activates the filament s heater until the desire
346. urce CIS Quadrupole Gas Analyzer manufactured by Stanford Research Systems is a differentially pumped quadrupole mass spectrometer specifically designed for the direct measurement of minute trace gas impurities in process gases at pressures below 10 mTorr In its most simple configuration an SRS CIS Analyzer consists of a CIS probe and an Electronics Control Unit ECU which mounts directly on the probe s feedthru flange and contains all the electronics necessary to operate the instrument The basic setup is shown in the following figure CIS Mounting Flange CIS Cover Tee To CIS lonizer N Pumping System Port Electronics Control Unit ECU CIS Quadrupole Probe Figure 1 SRS CIS Analyzer components The CIS Probe consists of a quadrupole mass spectrometer equipped with a high conductance differentially pumped CIS ionizer mounted inside a 2 75 Conflat Tee CIS Cover Tee The total probe equipment consists of three parts the closed ionizer electron impact the quadrupole mass filter and the ion detector I lonizer rc lon Filter co lon Detector l Feedthru Flange Figure 2 CIS Probe Components The side port of the CIS Cover Tee i e Pumping System Port provides the connection for the pumping group required to differentially pump the CIS ionizer and keep the quadrupole mass analyzer and the filaments at high vacuum during process monitoring CIS Quadrupole Gas Analyzer loniz
347. urned on to protect the delicate filament and CDEM from accidental overpressures Several commands can be used to trigger hardware tests on the ECU Any one of the internal checks just described can detect and report errors and it is the responsibility of the user to constantly monitor the CIS Head for error reports There are two ways to detect the presence of errors in the CIS Analyzer Visually Inspecting the red LED s on the rear panel of the ECU CIS Quadrupole Gas Analyzer 5 24 Programming the CIS Head The Error LED is turned on whenever a hardware problem is detected and it flashes twice if a communications error is generated during programming The Burnt and Leak LED s indicate specific filament problems and are turned on in addition to the Error LED whenever the ionizer s emission is internally shut down or not established as requested 2 Error Queries Queering the Error Bytes with the Error Reporting commands The Error Byte Definitions section of this chapter describes the different error bytes used to store the results of the internal checks The Error Reporting Commands query the error bytes and are used to quickly diagnose problems Important RGA Windows supports all the Error Reporting commands and routinely monitors the Error Bytes Detected errors are immediately reported to the user and identified based on Error Codes See the Troubleshooting chapter for recommended solutions to the problems The
348. used to generate a negative high voltage The multiplier output is compared to the set level HV SET by an error amplifier U800A which controls the voltage on the center tap of the primary via Q800 The primary current in the HV inverter is sensed by R814 a 2 2Q resistor If the primary drive exceeds 230 mA the output of the difference amplifier U800B will go positive reducing down the primary drive level The HV power supply piggy backs off the vertical interconnect PCB in between the top and bottom PCBs The HV power supply will only be installed in units which are ordered with the channel electron multiplier option CIS Quadrupole Gas Analyzer Chapter 10 Probe Assembly This chapter contains several CIS Quadrupole Probe assembly schematics In This Chapter CIS Quadrupole Probe Assembly Schematic eeeeeeeeesiseeseee nennen nean nennen nn nnn 10 3 CIS lonizer Exploded Schematic cccssccscecceseeeseseeeseeeenseeeeenesesneesesneeeesaeessaeseseeeenseeeeseeaeseaeseseeeseseaeas 10 4 Feedthru Flange Connectors Schematic ccssecceseeeeeseeeeneeseneeeeneeeeseaeseseaeseseeeeeeeeeseaeseseaeenseeeeeneaeas 10 5 CIS Quadrupole Gas Analyzer 10 2 CIS Quadrupole Gas Analyzer CEM anode N i MS INS t HV C W CDEM Anode Sse CH OO9 XC9 O Filament A Filament retum and lI supply Alignment rod Feedthru Flange Connectors LSI7 Slavd ONY AJIA O3007dx
349. vasive residual gases For other common interferences such as organic contaminants or reaction by products of the filament the gas tight design of the source reduces the visibility of the ionization region to those gases providing a very clean residual gas spectrum free of many of the spectral overlaps that are common in OIS PPR setups Interference from contaminants generated by ESD is also reduced in the CIS because a much smaller electron beam penetrates the ionizing volume In addition the inside walls of most commercially available CIS s are made out of highly inert materials such as gold platinum clad and pure molybdenum which adsorb less impurities than stainless steel Reduced lonizer Contamination In an OIS PPR system sample molecules that have suffered thermal cracking or chemical reaction at the filament are free to drift into the ionization region This is a very significant source of surface contaminants for electron impact ionizers In contrast the gas tight design of the CIS reduces the visibility of the source to those contaminant gases providing reduced contamination and better long term stability Most CIS manufacturers utilize exclusively Tungsten filaments in their systems W resists many corrosive gases such as WF and reactive gases such as Silane minimizing reactions at the filament that contribute to the background also resulting in extended filament lifetime Versatility CIS based systems are e
350. ve the recommended value of 70 Ls Ultimately the effective pumping speed is limited by the 50 Ls conductance of the 1 5 OD piping that connects the CIS probe to the pump Note 2 The CIS Analyzer is specifically designed for the direct measurement of minute trace gas impurities in process gases Detection limits in the 100ppb level corresponding to 10 Torr impurities in a 10 Torr process gas are not unusual Therefore a 10 Torr base pressure is a natural minimum requirement for the pumping system in order to minimize backgroung interferences in the mass spectra during ppm and sub ppm measurements CIS Quadrupole Gas Analyzer Chapter 4 Electronics Control Unit This chapter describes the most important features of the Electronics Control Unit of the CIS Analyzer In This Chapter due e Te To esed E 4 2 xen s 4 4 ee EEP TETEP E ETE cote sete atacae fetal cece ett cate actuated ege egene 4 5 F24VDC 2 5A CONN Clr eieiei egkleer Neger ENN eEe EE EN ege ENN eegEle EEN de aetier 4 5 RS232 DCE 28 8k Connector EE 4 6 Rz c 4 6 Locking ue e eroe Eee ette Lee Sale eet ae cea ecu e i Duque eue 4 6 Power entry module Option 02 eeeeseeesieeseeeeeeeeeeeeee nenne nnne nhan nn sain ant nn nn nn ann 4 6 LED Functionality eeni a AA E AEAEE E AA 4 7 STATUS Green KEES Det eebe Ee e ete Cea eee DEE Peg dee dee EA 4 7 ERROR Red EED S uno Peto ate dere eve end
351. ved in the non volatile memory of the CIS Head RI and RS commands respectively and used by the firmware to generate the internal scan parameters used to step the RF during scans and single mass measurements Please consult the Tuning Commands List in the Programming chapter of this manual for details on the RS and RI commands As described above the peak position tuning procedure requires the introduction of two known gases into the vacuum system A low mass gas 1 20 amu recommended is used to adjust the low mass end of the mass axis a high mass gas with a mass to charge ratio close to the upper limit of the scanning range of the CIS Analyzer is used to adjust the high mass end of the mass scale Several analog scans are performed and the values of RI RF Driver output 0 amu and RS RF Driver output 128 amu are adjusted until all mass peaks appear at the correct position in the mass scale An increase in RI causes the low end of the analog spectrum to displace towards lower masses A small effect is seen at the high masses An increase in RS results in the spacing between peaks in a scan to decrease with the largest effect seen at the high mass end The formulae used to correct the calibration parameters during peak position adjustment are presented next Low Mass Peak Position Adjustment To displace a low mass peak by a distance Am amu in the mass axis the value of RI must be modified from its original value RIo according to RI
352. ween adjacent peaks i e improves the abundance sensitivity of the spectrometer The location of the mass peaks and their widths can vary with time due to aging of the head Changes in resolution are particularly serious since they affect the sensitivity of the instrument and introduce errors in the partial pressure measurements The Peak Tuning procedures described in this section allow the user to calibrate the mass scale and the resolution Amjox of the mass spectrometer The CIS Analyzer has a very solid design and this type of tuning procedures should rarely be needed WARNINGS The peak tuning procedures should be performed by qualified personnel only A mistuned CIS Head will give Erroneous Readings until it is retuned properly Peak Tuning should only be attempted after the unit has been warmed up with the filament on and under typical operating conditions for at least a one hour Peak Tuning requires a mixture of gases whose mass spectra is well known In general a two gas mixture one with low mass peaks and one with high mass peaks is sufficient The sample is introduced into the vacuum and the quadrupole mass filter parameters referred to as Peak Tuning parameters are adjusted based on the sample analog spectra The mass scale is adjusted so that all peaks are displayed at their correct mass to charge values and the peak widths Am os are adjusted to unity or smaller values The two tuning procedures are referred to
353. when very precise numbers are desired one should obtain the appropriate fragment patterns by introducing pure gas into the instrument being used The fragment patterns must be obtained under the same conditions that will be used during regular spectral analysis since they depend on many instrumental parameters including electron energy emission current ionizer design mass filter settings detector type multiplier gain etc The principal mass peak of a fragmentation pattern is simply the most intense peak of the spectrum and the intensity of all the other peaks in the pattern are normalized to its height for the calculation of fragmentation factors Note that by our definition the Omg value for the principal mass peak of any gas is equal to one Principal mass peaks are used in the calculation of the sensitivity of the CIS Analyzer to different gases as shown below Partial Pressure Sensitivity Factors The partial pressure sensitivity of the CIS Analyzer to a gas g S g is defined as the ratio of the change H H in principal mass peak height to the corresponding change P P9 in total pressure due to a change in partial pressure of the particular gas species Ho and Po are background values S H Ho P Po The units of S g are of ion current per unit pressure amp Torr for example The sensitivity of the CIS Analyzer varies with different gases changes with time due to aging of the head and is a strong function of the op
354. wn above correspond to 1 Model number M MAX 100 for CIS100 200 for CIS200 and 300 for the CIS300 2 Firmware version for example 0 10 3 Serial Number of the unit 5 digit format The ID command is used for a variety of purposes e Make sure the CIS Analyzer is powered up and ready to go e Check the quality of the RS232 connection to the host computer e Check the user s communication software to make sure it is communicating properly with the CIS Head e Check the serial numbers of the CIS heads connected to the computer s serial ports The unique serial number attached to each head can be used for identification purposes avoiding the problems caused by cable swapping in the RS232 connections under multiplexed operation or head swapping in the vacuum system Parameters Only one possible format ID Error checking Only a query format is accepted Anything else results in a Bad parameter error Description Initialization command Echo STATUS Byte Initialize the CIS Analyzer to a known state Three different levels of initialization are available CIS Quadrupole Gas Analyzer Initialization Commands 5 29 Command excecution times vary depending on the pre existing ionizer conditions The end of the command excecution is prompted to the host computer returning the STATUS byte over RS232 Parameters INO Initialize communications and check the ECU hardware e The input and output data buffers ar
355. would significantly extend the time it would take the measurement to be completed e Please see the Peak Tuning section of the Tuning chapter for more details on mass axis calibration requirements under small and large temperature fluctuations in the CIS Head e The CA command turns off the RF DC voltages at the end of execution Parameters Only one possible command format is allowed CA Error Checking An attempt to pass any parameter with CA results in a bad parameter error being reported Description Calibrate Electrometer s I V response Echo STATUS error byte Perform a complete calibration of the electrometer s I V response The output of the electrometer is calibrated against input current over its entire operating range and a calibration table is stored in the non volatile memory of the CIS Head Instead of simply relying on the intrinsic logarithmic I V behavior of the electrometer a digital logarithmic interpolation algorithm calculates the currents from the calibration curve during measurements The procedure takes several seconds twice as long when the CDEM option is installed and its completion is signaled to the host computer by returning the STATUS byte value Important e The electrometer is designed for maximum long term stability however it is good practice to recalibrate it periodically particularly in the presence of a large change in the operating temperature of the CIS Head e All offset correction f
356. xact relationship between resolution and sensitivity is very complex as it depends on the concentration and divergence of the ion beam leaving the source It is complicated further by the defocusing action of the fringing fields between the ion source and the rods However as a general rule of thumb Sensitivity decreases at 1 to 1 5 times the rate of resolving power increase The inverse relationship between sensitivity and resolving power is also responsible for a very important feature of quadrupole mass filters operated at constant resolution The throughput of the analyzer decreases with mass Since AM ijo is constant the resolving power R MI AM io increases with mass reducing the effective throughput of the filter for high masses This effect must be taken into account when calculating partial pressure sensitivities from ion currents CIS Quadrupole Gas Analyzer 3 14 Quadrupole mass filter Zero Blast Suppression When the applied potentials are small or zero as at the beginning of a scan ions entering the filter may be transmitted even though their trajectories are mathematically unstable just because of the weakness of the fields and the finite length of the filter This gives rise to an output signal at the beginning of mass scans called the Zero Blast In the SRS CIS Analyzer the Zero Blast is suppressed preventing the DC voltage from reaching zero under 1 5 amu CIS Quadrupole Gas Analyzer Pumping System Requirements 3 1
357. xtremely versatile The low detection limit together with the wide dynamic range provided by the quadrupole mass filter fitted with an electron multiplier makes the CIS a versatile system for on line process monitoring and control verification of process gas purity at the point of use high vacuum residual gas analysis and process equipment leak checking Different modes of operation can easily be achieved by simply changing some of the sensor s operating parameters A CIS Gas Analyzer even though not as sensitive as an RGA can tackle most residual gas analysis and leak checking tests The sensitivity of the CIS is reduced over the OIS because of the very small holes for electron entrance and ion exit However in most cases this reduction in sensitivity is easily made up by running the electron multiplier at higher gain levels than the RGA The electron emission current is usually raised while using the sensor for residual gas analysis to increase sensitivity and reduced during process monitoring to avoid space charge saturation effects in the ionizing volume The tight design of the CIS also makes it possible to operate the ionizer at lower electron ionization energies than are possible with OIS s As a result most of the commercially available CIS systems offer two modes of operation with electron ionization energies of 70 and 35 eV The 70eV setting is mostly used for leak testing and routine residual gas analysis The spectra collected are vi
358. y factors for the three Basic Operating Modes of the CIS Analyzer RGA CIS 70 and CIS 35 modes Do not modify those memory locations if you plan to use RGA Windows to control the CIS Analyzer The three sensitivity factors are measured at the factory for N2 28 amu and stored in units of 10 A Torr before the unit is shipped out Please consult the General Operation Chapter of this manual for details on the Basic Operating Modes of the CIS Analyzer Important The numeric values stored in the Parameter Storage Table are not used internally by the CIS Head in any way during operation They can only be used by the software programs that operate the CIS Head from the host computer There is also two additional storage commands MV and MG that are used together to store CDEM specific information in the non volatile memory of the CIS Head MV CDEM High Voltage setting that corresponds to the gain stored by MG See MV command CIS Quadrupole Gas Analyzer 5 22 Programming the CIS Head MG CDEM gain at the HV setting stored in MV See MG command RGA Windows uses the stored MV value to bias the CDEM when the multiplier is turned on and the MG value as the corresponding gain while the multiplier is activated Important e The parameter values are not used internally by the CIS Head to correct for sensitivity or gain they are simply stored so they can be read and used by any computer connected to the spectrometer e MV and MG are only av
359. zer 4 10 Electrometer parameter setting available in the Scan Parameter Setups of the Scan menu is used to set the NF parameter value in the CIS Head according to the equation NF ScanSpeed 1 The following table summarizes the performance of the electrometer during mass measurements as a function of the Scan Speed and NF settings Please refer to this table to estimate minimum detectable partial pressures and scan rates for different scanning conditions Scan Speed NF Scan rate Single mass meas Baseline noise pc iue qt 2 1 1700 100 leld 3 4 3 20 2 2eld O pec pa s ee pt poe qacdy 2 0 2 5509 Jn poe i ml qul 95600 Le o mc cg 49 x 65 E a The values in this column are the result of averaging a large number of data points from several different units Use this values for reference only Variations are to be expected from unit to unit as a function of operating conditions and even as a function of time Adjusting the Zero of the lon Detector The zero of the ion detector is automatically readjusted at the beginning of each analog and histogram scan so that the baseline is always centered around zero The zero can also be readjusted at any time with the command CA In both zeroing procedures the output of the electrometer is measured in the absence of input ion current and stored as a current value in the instrument s memory The current value called offset cor

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