High power impulse plasmas for thin film deposition - dbs-lin
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1. end of the resistor string is attached to the positive high voltage and the other end of the string is grounded The dynodes maintained at increasing potential create a series of amplifications When a particle e g ion strikes the first dynode it generates secondary electrons The secondary electrons are then accelerated into the next dynode where each electron produces more secondary electrons thus generating a cascade of secondary electrons Typical amplification is of order 10 generated electrons per one incoming particle 6 7 Mass analyzer separates the ions according to their mass to charge ratio All mass spectrometers are based on the dynamics of charged particles in electric and magnetic fields in the vacuum where the Lorentz law and Newton second law applies F ma 2 where F is the force applied to the ion q is the ion charge E is the electric field v xB is the vector cross product of the ion velocity and the magnetic field m is the mass of the ion and dis the acceleration Equating the eq 1 and eq 2 the expressions for the force applied to the ion yields G E 0xB 1 3 where m q is called mass to charge ratio Initial conditions of the particle and equation 3 are completely determining the particle motion in space and time Two particles with the same mass to charge ratio m q behave the same This is the basic principle of mass spectrometry The quadrupole mass analyzer QMA Figure 10 con2. increasing it or decreasing it in MODIFY menu External trigger _ TN AB channel A 4 18 3 Exercises The aim of the F praktikum is to perform characteristic measurements of the ions in plasma using mass spectrometer The mass scan provides information on particles that can be found in the plasma by scanning over mass to charge ratio with fixed energy Time averaged energy measurement performs a scan over energies for fixed mass to charge ratio resulting in the ion energy distribution function IEDF The scan accumulates the signal for 300 ms for each energy point With pulse duration of 200 us and repetition of 50 Hz and 100 Hz the scan collects over 15 or 30 pulses depending on frequency Meaning ions arriving both during the pulse and between the pulses are recorded and it represents the IEDF of ions arriving to the substrate where thin film is deposited In order to understand the origin of different energy groups of the IEDF time resolved measurements at points during the pulse shortly after the pulse and in between the pulses is recorded Furthermore the scans will be measured for two discharges in order to understand the influence of the power on the IEDF of Ar and metal ions The experimental part starts by venting the vacuum chamber and repositioning the magnetron in order to position it facing mass spectrometer at distance of 15 cm Once the magnetron is mounted the chamber is pumped down to a base pressure of 5x10
3. increasing thermal loads on the target The main advantage of HIPIMS over DC magnetron sputtering is increased ion to neutral metal ratio Increase in the ion to neutral ratio of Cr triangles and circles and increase in the ion current density and deposition rate squares with increase of target current Figure 5 At peak target currents of around 25 A ration of Cr and Cr is 1 indicating 50 ionisation of sputtered material The increase in the ion to neutral ratio is the consequence of increased electron density in the target vicinity On Figure 6 linear dependence of the electron density on the peak discharge current is shown The time and spatial evolution of the electron density was measured revealing electron 3 densities above 10 m The results presented on Figure 7 show electron densities above 10 m in the chamber even at 640 us from the start of the pulse 6 0 1 Arbitrary Units 0 01 10 Peak target current A Figure 5 Ion to neutral ratio and deposition rate as a function of target current Triangles represent I Cr Cr circles represent I Cr Cr and Squares represent the ratio of 10n current density to deposition rate Peak plasma density 10 m 10 20 30 40 50 60 70 80 90 Peak discharge current A Figure 6 Plasma density as a function of peak discharge current in the HIPIMS discharge Electron density t 40us 50 25 j 25 20 20 15 is gt 1E19
4. is kept at a constant negative voltage Positive ions generated in the plasma are accelerated towards the cathode sputtering atoms and molecules from the target surface Secondary electrons are emitted and accelerated away from the target surface as a result of the ion bombardment Secondary electrons are confined in the magnetic field near the cathode Metal from the target is sputtered by ion bombardment and ionised by electron impact ionisation DC magnetron sputtering is a line of sight process since it generates mostly neutral atoms whose trajectory and energy cannot be easily controlled therefore rather low pressures are used to minimize scattering of the sputtered atoms 1 Diffusion of the electrons and ions in the DC magnetron sputtering through the chamber shown on Figure 3 shows similar spatial density distribution of electrons and ions that supports the theory of plasma quasi neutrality 22 electron ion 0 0 0 z cm 12 6 z cm 12 Figure 3 Simulated electron and ion distribution in the space near the target 1 3 Influence of adatom mobility on the film density DC magnetron sputtering improved deposition rate and quality of the coating compared to glow discharge However the simulations done by Muller 8 showed importance of the adatom energy on the microstructure of deposited coating He investigated adatom migration effects using microstructure evolution growth simulation Muller found that above a critical tempera
5. particles sputtered from the target is Thompson distribution Thompson distribution describes the energy spectrum of ejected atoms during sputtering process Fr E 2 1 5 a Where E is energy of the ejected particle E is surface binding energy of the AEit EptE 3 eM with M and M are the masses of i a target material E is maximum recoil energy and A the incident atom and the sputtered atom Metal atoms are ionized through electron impact ionisation Diffusing from the target metal ion collides among themselves and with Ar ions and atoms resulting in the thermalisation of metal ions The energy scale measured by mass spectrometry is represented in volts To change the energy scale to eV it is necessary to multiply it by the charge of the particle e g in case of doubly charged ions the energy scale should be multiplied by two to obtain the energy scale in eV 1 5 1 Time averaged mode Mass spectrometer acquires data at certain energy for a specified length of time Changing the acquisition time it is possible to measure the IEDF in time averaged and time resolved mode In the time averaged mode the acquisition time is in order of several hundred milliseconds meaning the detector was collecting the ions arriving to the detector for 300 ms which is at frequency of 20 Hz around 6 pulses The amount of ions detected at certain energy represents the number of ions detected both during and between the pulses The IEDF meas
6. the powers supply that consequently increases the current By applying higher powers higher thermal load is applied 14 to the target and in order to reduce the thermal load during discharge 2 frequency should be reduced Following images show expected discharge waveforms Tek ale Acq Complete M Pos 152 005 ACQUIRE Tek Me Acq Complete M Pos 152 005 CURSOR 1 1 Type Sle aiia a SOurce fee so oe Averages Cursor 1 d 0 008 2 CHT 200 CHE 5 004 M50 0us Ext 3 18 CHT 200 CH2 5 004 MM 50 0us Ext 3 18 20 Mar 12 1315 100 006H2 20 Mar 12 1323 50 0026H2 Discharge 1 Discharge 2 2 2 MassSoft Templates for mass scan Mass scan exp time averaged measurements time averaged exp and for the time resolved measurements time resolved exp can be found in the folder C Dokumente und Einstellungen ep2 Eigene Dateien Mass Spectrometer EQP Template Student Scan starts by clicking on to the green round button in the program menu MASsoft Professional File Edit MassSpecs Tune System Views Applications Window Help Ome amp amp y g EB E JEI E S E EREE Ae Scans can be exported to csv file for plotting and analysis Unfortunately scans can be saved only one by one Click on the scan you want to save and go to File gt Export gt File and save the scan Repeat the steps for all scans 15 HE MASsoft Professional mie Edit MassSpecs Tune System Views Applications Window Help Clos
7. 10 10 5 5 5E18 10 5 5 10 10 5 5 10 y om y iem d 1E18 a t 280 us os 9 20 5E17 5 10 1E17 5 10 5 0 5 10 2E gt 0 5 10 5E16 y cm y cm Figure 7 Temporal and spatial variation in the electron density below the target at 40 160 280 and 640 us after pulse ignition High powers in the pulse result in amplified sputtering of the target Increased density of sputtered material in the target vicinity and momentum transfer from sputtered particles to Ar particles leads to effect called Ar rarefaction The effect of Ar rarefaction is presented on Figure 8 The results show substantial Ar rarefaction with gas density reduced tenfold in the close vicinity of the target O70 194 19 EADE 18 7 e eS06 60e 19 e4 E ii 0ery o 10E 194 e 20E 10 08 19 10E 19 208 19 00 06 00 1 0e 19 Figure 8 Time evolution of Ar gas density of in m On the left side is the target x is the distance from the target and time on the top of the image represents time within the discahrge The IEDF of metal and Ar ions in HIPIMS obtained using plasma sampling mass spectrometry showed that during the pulse a Thompson like high energy tail distribution of metal IEDF with energies up to 100 eV has been reported Whereas after the pulse metal ion IEDF comprised of a main low energy peak and a high energy tail for measurements recorded in the vicinity of the target Time resolved measurements comparing the rise of the discharge
8. High power impulse plasmas for thin film deposition Fortgeschrittenen Praktikum Ruhr Universitat Bochum Ante Hecimovic 23 March 2012 The Electrostatic Quadrupole Plasma EQP Mass Spectrometer is an experimental instrument used to measure the ion energy distribution function of atoms and ions in the plasma and to perform the mass analysis of the plasma In this practical course the student will investigate the ion energy distribution function IEDF of metal and Ar atoms in High power impulse magnetron sputtering HIPIMS plasma discharge Students should already pass introduction in the plasma physics 1 Table of Contents 1 Theory 1 1 Magnetron sputtering 1 2 Direct current DC magnetron sputtering 1 3 Influence of adatom mobility on the film density 1 4 High power impulse magnetron sputtering HIPIMS 1 5 Plasma sampling mass spectrometer 1 4 1 Time averaged mode 1 4 2 Time resolved mode 2 Instrument manuals 2 1 HIPIMS power supply 2 1 1 Setting the apparatus 2 1 2 Setting the parameters 2 1 3 Discharge parameters 2 2 MassSoft 2 2 1 Mass scan 2 2 2 Time average energy scan 2 2 3 Time resolved energy scan 2 3 DG 645 Delay generator 3 Exercises 4 References 12 12 13 13 13 14 16 17 17 18 19 22 1 Theory 1 1 Magnetron sputtering Gas discharges can be initiated when the voltage across the electrode is equal to or exceeds the static breakdown voltage gap V Increase in voltage results in an abr
9. current to the end of the pulse have shown the existence of a single low energy peak in the post discharge Several papers used mass spectrometry to describe the influence of pressure on the IEDF and the influence of power on the IEDF Increasing the working gas pressure the high energy tail of the metal IEDF was reduced and the low energy peak of the metal IEDF increased and narrowed as a result of thermalisation The OES measurements of HIPIMS of Cr showed that in the beginning of the pulse the plasma is dominated by Ar atoms and Ar ions At the peak of the discharge current Cr atoms and Cr and Cr ion signals appear The intensity of the Ar species signal drops with the discharge current and the Cr signal dominates the end of the pulse After the end of the pulse the Cr signal drops and the Cr signal is dominant The ion saturation current measured at different distances from the target showed that ions are able to leave the magnetized region and reach the substrate in greater numbers depending on the peak current which is the consequence of the kinetic pressure exceeding the magnetic pressure 8 1 5 Plasma sampling mass spectrometer The mass and relative concentrations of atoms ions and molecules and their energy distribution is measured using plasma sampling mass spectrometer Schematic picture of plasma sampling energy resolved mass spectrometer showing main parts is shown on Figure 9 Quadrupole lens vert hor
10. e Close All Le Save Save Ag Save s Template Export Import Convert File Ri Unlock 2 2 1 Mass scan wN Eda CCE FOO Ow naza M Ctrl 0 Wokumente und Einstellungen ep tigene Dateien Mass Spec Einstellungen ep Eigene Dateien Mass Spectrometer EQP F p ind Einstellungen ep tigene Dateien Mass Spectrometer EQP und Einstellungen ep igene Dateien Wass Spectrometer EQ istellungentep tigene Dateien Mass Spectromete HAL 7 EQ Ctrl U Typical Mass scan is shown in the following picture recorded at energy of 2 eV with strong peak at 40 amu representing Ar and accompanying isotopes Peak at 52 amu is Cr peak at 20 amu is Ar m q 40 2 and small peak at 26 amu is Cr m q 52 2 i MASsoft Professional File Edit MassSpecs Tune System Views Applications Window Help De E PBAasr 2R SQli eB a m HAL 7 EQP HIGH ENERGY 13349 C Dokumente und Einstellungen ep 2 Eigene Dateien Mass Spectrometer EQP 1 amplate Mass scan exp Available sqe jonuog cE Z e Ooewi ssaetne Y Scan 1 Mass scan C Dokumente und Einstellungen ep2 Eigene Dateien Mass Spectrometer EQP Tamplate Mass scan exp View 1 SEM cls 80000 70000 60000 50000 40000 30000 20000 10000 0 0 Cycle number 1 HAL 7 EQP HIGH ENERGY 13349 mass amu HAL 7 EQP HIGH ENERGY 13349 E onsiMs F1 F2 Enmission multiplier 1600 energy 13 80 V New All time resolved testl4 exp Mass sca
11. e DG 645 Delay Generator The delay generator uses TTL signal from the power supply as a trigger and creates a new TTL signal where value set at the A edge sets the delay between the power supply trigger and new TTL signal basically the desired time delay Value at edge B is the width of anew TTL signal The new TTL signal is used to trigger the Mass spectrometer detector Minimum acquisition time at the detector is 1 ms By setting the width of new TTL signal to 10 us meaning time resolution is 10 us the measurement will be accumulated over 100 17 pulses 100 x 10us 1 ms Consequently setting the width to 20 us the signal will be accumulated over 50 pulses 2 3 DG 645 Delay generator DISPLAYED PARAMETER RIG RATE TRIG THRES DISPLAY mo E STATUS TIMEBASE gt INTERFACE Rem act Switch the power button on the right bottom side of the delay generator Connect external trigger and define the trigger edge by scrolling up and down with the arrows in the TRIG MODE Plug the cable for the new delayed trigger in either AB CD EF or GH channel Example AB channel o Scroll EDGE until you reach A channel o To adjust the delay of the A edge use CURSOR to reach the digit you want to alter o Change the digit by increasing it or decreasing it in MODIFY menu o Now Scroll EDGE until you reach B channel to change width of the new channel o Use CURSOR to reach the digit you want to alter o Change the digit by
12. ectrons would be trapped An axisymmetric dc magnetron discharge configuration is shown on Figure 1 b A discharge is formed when a negative voltage of 200 V or more is applied to the cathode Plasma in the magnetron discharge will be seen as the bright circular plasma ring of width w and mean radius R The sputtering will occur in a track below the plasma and the area with eroded sputter profile is called racetrack The plasma shields the electric field through most of the chamber and a cathode sheath s of the order of several Debye lengths develops which sustains most of the externally applied voltage Due to the high mass magnetic field doesn t confine working gas ions in the plasma which are accelerated toward the cathode and strike it at high energy In addition to sputtering material the impact of the ions produces secondary electron emission These electrons are accelerated back to the plasma and are confined near the cathode by the magnetic field The electrons undergo a sufficient number of ionizing collisions to maintain the discharge before being lost to a grounded surface 2 3 Both electric and magnetic field are present in a magnetron discharge The electric field accelerates electrons away from the cathode and ions towards the cathode Magnetic field has a circular shape from the edge towards the centre of the cathode The Larmor orbit of electrons is small compared to curvature of the magnetic field thus electrons follow magnetic lines a
13. ew York 2003 3 D S Rickerby and A Matthews Advanced Surface Coatings Blackie amp Son 1991 4 K Sarakinos J Alami S Konstantinidis Surface and Coatings Technology 2010 Feb 25 204 11 1661 84 5 Hiden analytical EQP User s manual 6 D A Skoog F J Holler and T A Nieman Principles of Instrumental Analysis Harcourt Brace College Publishers 1992 7 B Henning and J Holger Surface and Thin Film Analysis A Compendium of Principles Instrumentation and Applications Wiley VCH 2003 8 K H Muller J Appl Phys 62 1796 1987 22
14. generate the HIPIMS plasma discharge Power supply is operated manually over the display located on the DC unit In order to ignite the plasma several parameters must be set These parameters are Voltage Frequency Pulse duration Max charge Parameters of the HIPIMS discharge are set using control panel mounted on the DC unit On the control panel menus are changed by menu button to either o Voltage menu Uout or o Power menu POWER OFF 13 Voltage menu o In voltage menu scroll down to ACCESS CODE and change from 0 STRD to 1 SETP In SETP mode two more menus are available but are not used USER SETUP MENU and HUETTINGER menu o Scroll up and adjust the voltage Power menu o Change pulse frequency at PLS FREQ 2x 25 Hz that is 50 Hz and only number 25 can be changed max 500 Hz o Change pulse duration PULSE TIME 200 us max 200 us o Scroll up and change POWER from OFF to ON Reminder for switching the setup off o Switch the plasma off o DC and pulsing unit o Oscilloscope and current probe o Magnetron cooling o Flow and flow controller unit 2 1 3 Discharge parameters Student should investigate the influence of discharge power on the IEDF of Ar and Cr particles For this purpose two discharges are compared Discharge parameters for each discharge are given in the s table a a a sow pa e e v p_ e E woo e e R Lc a Discharge power is elevated by increasing the voltage on
15. gy groups in the time averaged energy measurement Set parameters for discharge conditions with 25 A Measure the IEDF of Ar Ar Cr and Cr ions for three points in time 220 us 380 us and 600 us Extract the data into csv file For report Protokoll Plot time averaged measurements and time resolved measurement of each species on the same graph to recognise the origins of certain ion groups Pay attention to the fact that acquisition lengths were different Comment on the shapes of IEDF regarding the times it was measured and recognise Ar rarefaction enhancement Discuss difference between Thompson and Maxwellian distribution Explain the results taking into account Ar rarefaction and thermalisation of the particles One third of the report should consist of introduction and two thirds should be description of your experiment and discussion of the results Apart from the discussion relevant to the samples that you have investigated you can use the following set of questions to help you shape your report 20 What is magnetron sputtering What is HIPIMS What are the main principles of the Electrostatic Quadrupole Plasma EQP Mass Spectrometer What information can we obtain using the Mass spectrometer 21 4 References 1 M A Liberman and A J Lichtenberg Principles of Plasma Discharges and Materials Processing John Wiley and Sons Inc New York 1994 2 W D Westwood Sputter Deposition AVS N
16. iz D C quad EQP extractor lens2 Energy filter plates a F4 Orifice A eee eee 1 i js Ba lms 5 LTT HENS BE es l i IL ca POA L N i PZ lens1 axis LL Mass filter resolution delta m lonisation source emission electron energy cage energy transit energy suppressor Detector multiplier 1st dynode discriminator Figure 9 Schematic of the mass spectrometer 5 The ions are extracted from the plasma and focused by applying direct current voltage on the extractor electrode and by the lens electrode Voltages on the extractor electrode and on the lens electrode are around 10 V and 79 V respectively Negative voltage on the extractor is used to repel electrons and accelerate ions In the next step it is possible to choose Residual Gas Analysis RGA mode that uses internal impact ionisation source for ionisation of neutrals from the plasma In this practice RGA mode was not used since only ions generated in the plasma were analysed The ions from the extraction electrodes are then filtered by the energy filter Remaining ions are further filtered by their mass to charge ratio in the quadrupole mass analyzer QMA Ions with the selected mass to charge ratio are detected in the detector The secondary electron multiplier SEM is used as an ion detector A secondary electron multiplier consists of a series of electrodes called dynodes each connected along a string of resistors One signal output
17. mbar 3 1 Mass scan Goal Observe particles that are present in the HIPIMS discharge Find most representable energy at which to conduct the mass scan Task Run the time averaged scan for discharge condition with 5 A to find the peak energy of the IEDFs Recognise 2 peaks and perform mass scan for both peaks Repeat the procedure for discharge condition with 25 A and extract the data into csv file For report Protokoll Recognise the ions from the mass scan including associated isotopes Discuss the intensities of Ar and metal ions both for singly and doubly charge ions Comment on the change of the intensities of the peaks for two scan energies Comment on the change of the intensities when increasing discharge power 19 3 2 Time averaged energy measurement Goal Task Understand influence of discharge power on the shape and intensity of IEDF and changes in the energy span Measure the IEDF of Ar Ar Cr and Cr ions for two discharge conditions Extract the data into csv file and plot the data with aim to compare the IEDF of one species at different discharge powers For report Protokoll Discuss relevant intensities and shapes of different species Comment on the change of the IEDF when increasing discharge power Integrating IEDF over the energy calculate the ion fluxes and plot them as a function of power 3 3 Time resolved energy measurements Goal Task Understand origin of different ener
18. n exp Acquisition in progress EaR Mass scan performs scan at fixed energy that is usually a few eV since it is expected that majority of ions is thermalised and peak of the ion energy distribution function lays at 1 or 2 eV 16 2 2 2 Time average energy scan Typical Energy scan is shown in the following picture The scan tree window contains four 2 2 energy scans for Ar Cr Ar and Cr iE MASsoft Professional File Edit MassSpecs Tune System Views Applications Window Help Oe SB s i E CIEI A A E E r nE G zz HAL 7 EQP HIGH ENERGY 13349 C Dokumente und Einstellungen ep2 Eigene Dateien Mass Spectrometer DE Scan 3 Ar 2 C Dokumente und Einstellungen ep2 Eigene Dateien Mass Spectrometer EQP Tamplate time Belk SEM cls HAL 7 EQP HIGH ENERGY 13349 sqe jonuog 10 energy V 0 l 20 20 40 energy V 20 40 0 10 Cycle number 1 energy V Cycle number 1 eae HAL 7 EQP HIGH ENERGY 13349 New All time resolvedtest18 exp time averaged exp E ionsiMs F1 F2 Emision multiplier 2100V energy 430 V Acquisition in progress 2 2 3 Time resolved energy scan The time resolved measurements are same as the time averaged measurement with difference that measurements are triggered Custom cable should be plugged in AUX I O MSC 05 port at the back of the Mass Spectrometer Interface Unit on one side and the other BNC side should be plugged in the AB channel of th
19. nd are being entrapped in the magnetic field This enables longer path lengths of electrons and increases the number of ionisation collisions The magnetic field lines of the magnetron could be set up as completely closed known as balanced magnetron Figure 2 a or closed in the middle and open at the edge of the magnetron called unbalanced magnetron Figure 2 b Balanced magnetrons have magnetically trapped electrons and low ion flux to the substrate which is advantageous for deposition of thin films on polymer substrates since it cannot withstand high ion flux density created in the unbalanced magnetron In the unbalanced magnetron ion flux to the substrate is increased as well as ionisation of metal atoms in vicinity of the substrate Unbalanced magnetrons are advantageous for hard coatings 2 a b Magnetic field lines Permanent ee Permanent magnets magnets Se Target a e ec Water cooled Water cooled cathode cathode Figure 2 Schematic of the a balanced magnetron with closed magnetic field lines and b unbalanced Magnetic field lines N z i Z4 magnetron with magnetic field lines open at the edge of the target from 1 4 1 2 Direct current DC magnetron sputtering Direct current DC magnetron sputtering is a sputtering technique that uses magnetic fields to enhance and confine the plasma mainly electrons in the target vicinity In a conventional DC plasma discharge the cathode
20. ratio On Figure 11 it is possible to recognize main isotopes of chromium Cr at m q 52 and Argon Ar at m q 40 The unified mass unit of Cr isotope is 52 and once ionized Cr ion has q 1 thus mass to charge ratio m q for Cr is equal to 52 On Figure 11 one can recognize stable Chromium isotopes Crs m q 53 and Crs4 m q 54 and long life isotope Crs m q 50 with half life of 1 8 e 17 y 30 Twice ionized ions have q 2 thus Cr has m q 26 and Ar has m q 20 On Figure 11 peaks for Cr with m q 26 and Ar with m q 20 can be seen 100000 10000 i Co So Intensity counts s 0 5 10 15 20 25 30 35 40 45 50 Energy eV Figure 12 Ion energy distribution function for Cr in Ar atmosphere at pressure p 0 29 Pa The energy distribution of Cr ion is measured by setting QMA to enable only ions with m q 52 and then scanning all energies using the energy filter Figure 12 shows an example of the Cr ion energy distribution in Ar atmosphere at pressure of 0 29 Pa 11 The initial IEDF for Ar ions differ from metal ion energy distribution Before the pulse Ar particles are in thermal equilibrium thermalised at room temperature at 300K Maxwell distribution describes the energy spectrum of particles in thermal equilibrium Fy E 2 exp 1 kpT kpT where E is the energy of the particle kg is Boltzmann constant and T is the temperature of the system Distribution of metal
21. sists of four parallel metal rods Each opposing rod pair is connected together and a radio frequency R F voltage is applied between one pair of rods and the other A direct current voltage is then superimposed on the R F voltage Ions travel between the rods and through the quadrupole Only ions of a certain mass to charge ratio will reach the detector for a given voltage parameters Other ions will be lost due to collisions with rods and the wall of QMA This allows selection of a particular ion or scanning by varying the voltages Detector resonant ion Source de and ac voltages Figure 10 Schematic of the quadrupole mass analyzer showing resonant ion passing the analyzer and reaching the detector and nonresonant ion scattered in the analyzer In this practice the plasma mass spectrometer was used for two purposes First was measuring mass spectrum of the plasma Second was measurement of the ion energy distribution An example of a mass spectrum of a HIPIMS of Cr discharge is shown in Figure 11 10 200000 150000 100000 Intensity c s 50000 0 10 20 30 40 50 60 Mass to charge ratio Figure 11 Mass spectrum of HIPIMS plasma discharge for Cr target in Ar atmosphere taken at an ion energy of E 0 5 eV at pressure of p 0 29 Pa Mass spectrum is measured by setting a fixed voltage on the Bessel box to define the ion energy and changing the voltage on the QMA therefore scanning through the mass to charge
22. ture range the porous columnar microstructure changes to a configuration of maximum packing density Figure 4 Film deposited at 350 K shows columnar structure Increasing deposition temperature from 350 K to 420 K film densifies but columnar structure is still visible Increasing deposition temperature to 450 K fully dense film is deposited with local defects Apart from heating the substrate energy can be 5 conveyed by energetic ions impinging onto the substrate Using negative bias on the substrate energy of impinging ions can be controlled Disadvantage of DC magnetron sputtering is low ionisation of sputtered metal Therefore metal particles arriving to the substrate comprise mainly neutrals that are not affected by substrate bias The ionisation of sputtered metal can be increased by increasing the discharge power however thermal load onto the target get increased that can lead to melting of the target Figure 4 Two dimensional microstructure simulation of Ni films deposited as a function of temperature from 61 1 4 High power impulse magnetron sputtering HIPIMS In 1999 a method was suggested where high power is delivered to the target in short pulses 100 us with repetition frequency of 100 Hz and duty cycle of 1 By pulsing the target voltage a lot of power is delivered to the target that generates high ionisation of sputtered metal portion and low duty cycle imply average powers being comparable to the DC powers without
23. upt increase in current which is accompanied with an increase in glow intensity in the gap DC glow discharges have long been used as sputtering sources for metallic materials Figure 1 a illustrates planar DC glow discharge driven by a constant current dc source 1 The upper electrode which is a cathode serves as the target for ion impact sputtering The substrate on which the sputtered atoms are deposited is placed on the lower electrode which is the anode Cathode Dark space Lic 1 Vac i Negative glow Substrate al b Figure 1 Schematic of a DC glow discharge and b DC magnetron discharge adapted from 1 The discharge is maintained by secondary electron emission from the cathode with the energetic secondary electrons providing the ionization required to maintain the discharge However operating pressures must be high enough p gt 4 Pa 30 mTorr so that secondary electrons are not lost to the anode or side walls This pressure is higher than optimum for deposition of sputtered atoms onto the substrate due to scattering of sputtered atoms The drawback of the DC glow discharge is the low sputtering power efficiency which is decreasing with increasing energy It is necessary to operate a sputtering discharge at higher densities lower voltages and lower pressures In order to confine the secondary electrons permanent magnets were placed behind the cathode to create the closed magnetic field lines where the el
24. ured in the time averaged mode gives information of ions arriving to the substrate during deposition 1 5 2 Time resolved mode In the time resolved mode the acquisition time is set to 20 us and the detector was triggered from the power supply trigger From the orifice of the mass spectrometer till the detector the ions need to go through the different parts of the mass spectrometer and the required time is called a time of flight TOF The TOF ms through the spectrometer is determined by the velocity of ions through its separate sections which are characterised by different accelerating or decelerating voltages Calculator for the TOF for various species is given in excel file Transit xls 12 2 Instrument manuals 2 1 HIPIMS power supply 2 1 1 Setting the apparatus Following apparatus should be running in order to run the HIPMS discharge Gas flow o Switch on the MKS PR 4000 o Check that the both vents on the gas bottle are open o Adjust the flow o Switch the flow on and check the pressure on MKS PR 4000 mounted in the Vacuum pumps control rack Power supply o Switch the power supply rack Pulse unit is automatically switched on o Switch the DC unit Monitoring system o Switch the current probe on o Switch the oscilloscope on o Check the voltage probe is connected on the back of the power cable plug o Switch the magnetron cooling on 2 1 2 Setting the parameters Huttinger TruPlasma Highpulse 4002 is the power supply used to
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