Operating Instructions - University of Notre Dame
Contents
1. 3 The 225 current source 1 Power switch turned off Voltage compliance set to 50 volts Output selector set to either of the standby positions Decade switched set to 1 0 0 Range set to left most mA position 6 Filter off 4 Turn on the 225 current source 163 DMM and the 530 Type All system 1 Allow 30 minutes for warm up 1 Ifthe sample dimensions are not know it is recommended to measure the dimensions of your sample during this warm up time 1 Sample thickness in cm 1 mil 0 00254 cm 1 5 mil 0 0127 cm 2 10 mil 0 0254 cm 3 20 mil 0 0508 cm 4 30 mil 0 0762 cm 2 Sample 1 Diameter if round in cm 1 2 inches 5 08 cm 2 3 inches 7 62 cm 3 4 inches 10 16 cm 2 Length and Width if rectangular in cm Shar BASAN 5 Place the test sample on the glass plate and center the sample under the probe head 1 Rectangular samples should be tested with the length parallel to the probe tips BPI 2 Circular samples should be tested with the probe tips centered on the sample P N OHH J NN we et 6 Lower the probe head by moving the chrome handle down Once at the bottom of the handle travel slide the handle to the left so to lock it in the lowered position Keith Darr Rev 1 0 10 31 2008 Connection Check Verify that the current source has a value of 1 00 mA selected Switch the output selector on the current source to the position Verify on the 530 Type All system that the 1K2. t in cm to the probe tip spacing s incm Probe tip spacing s 50mil 0 127 cm in this application Ratio of the sample diameter d if round or the width d as used in chart 1 if rectangular to the probe tip spacing in cm s 0 127 cm in this application C is found directly from chart 1 Sheet resistance correction factor for circular and rectangular samples Slice resistance Slice resistance as a function of the geometric correction factor F and the spreading resistance Rsp Geometric correction factor derived for round samples used to find slice resistance p Correction factor used to calculate slice resistance p as a function of the ratio of probe tip spacing to sample diameter derived from table 1 Thickness correction factor as a function of the ratio of thickness to probe tip spacing Derived from table 1 Used to calculate slice resistance p Sheet resistance R as a function of slice resistance p and sample thickness in cm Sheet resistance R with a correction factor C derived from chart 1 Length of a rectangular sample in cm Width of a rectangular sample in cm Conversion factor between mil and cm measurement units 11 Referenced Works Thickness correction factor for a four point probe on an infinitely large sample horizontally Data from L B Valdes Resistivity Measurements on Germanium for Transistors Proc IRE 42 2 420 427 Feb 1954 1954 IEEE ASTM F 84 99
3. 100 mV position 2 The LO and the HI banana plugs should have a shorting device connected to the respective plugs on the 530 Type All system and the voltmeter 2 The 530 Type All system 1 Function set to standby 2 Power switch off 3 Probe set to A 4 Current shunt set to 1K 3 The 225 current source 1 Power switch turned off Voltage compliance set to 50 Output selector set to either of the standby positions Decade switched set to 1 0 0 Range set to left most mA position Filter off ON ut es BS Sample requirements 1 The sample under test must meet the following requirements to be tested using the four point probe a The sample under test must be on top of an insulating layer unless the thickness t of the sample under test is greater than 5 times the probe tip spacing 5 s i This is a thickness t value greater than 250 mil 0 635 cm thick when using a probe tip spacing of 50 mil 0 127 cm as in the case of this piece of equipment 1 Ifthe thickness t of the sample is greater than 5 times the probe tip spacing s the sample is viewed as being infinitely thick to the four point probe and no thickness correction factor F t s will be needed for sheet and slice resistivity calculations ii The sample may be a a bare semiconductor sample or a relatively thin layer in respect to the probe tip spacing t lt lt s such as an implanted or diffused layer if that layer is of different majority carrier that that of the under
4. 5 4 322 0 080 4 294 0 085 4 265 0 090 4 235 0 095 4 204 0 100 4 171 Values that fall in between displayed values can more correctly approximated via the following method Keith Darr Rev 1 0 10 31 2008 If s d 0 053 s d F 0 050 4 436 0 055 4 417 F 0 050 0 055 4 436 4 417 0 050 0 053 4 436 4 437689 Sheet Resistance Rs Sheet resistance R can be simply calculated as a function of the slice resistance p and the sample thickness t However when testing rectangular samples this procedure requires that the sheet resistance R be found before the slice resistance p which will then become a function of the sheet resistance R and sample thickness t R p t 7 R C V D l WwW R C V D Q sq Sheet resistance R as a function of slice resistance p an sample thickness cm Thickness of the sample expressed in cm none Sheet resistance correction factor R for circular and rectangular samples as derived from chart 1 Q sq Sheet resistance R for circular and rectangular samples C is found directly from chart 1 cm Length of a rectangular sample in cm cm Width of a rectangular sample in cm Q sq Sheet resistance R of a rectangular sample when a lt 2d where a length and d width as in chart 1 see note Chart 1 Used to calculate sheet resistance R for circular and rectangular samples Note When a rectangular sam
5. Equipment Required none Materials Required Semiconductor sample of a known geometric dimensions which meet the requirements defined in this procedural document Protective Equipment Required Latex Gloves Safety glasses Engineering and or Administrative Controls Only authorized users may operate this piece of equipment Training To obtain training on this machine please contact Keith Darr office 221 phone 1 5497 email kdarr nd edu Problems For problems clarification of procedures or general information pertaining to this machine please contact one of the following personnel Keith Darr 631 5497 Kdarr nd edu Mike Thomas 631 7493 Thomas 20 nd edu Mark Richmond 631 6478 Richmond 7 nd edu In Case of Emergency Please Contact Notre Dame Security at 911 MSDS s can be located in the EE Department office or in Room 244 near the door Keith Darr Rev 1 0 10 31 2008 Table of Contents Page Contents 4 Authorized Users List 5 Standby Conditions Sample requirements 6 Equipment Setup and 7 Connection Check Resistivity Measurement 8 Resistivity Measurement Conductivity Type Procedure 9 Slice Resistance p Calculation 10 Sheet Resistance R Calculation 11 Formulas and variables 12 Referenced Works Keith Darr Rev 1 0 10 31 2008 Authorized Users List Name Email Advisor Date Keith Darr Rev 1 0 10 31 2008 Standby Conditions 1 The 163 digital voltmeter 1 Inthe
6. Four Point Resistivity Probe Operation Probe base Kulicke and Soffa Industries Inc Model 3007 Resistivity Probe Base Electronic Circuitry Keithley Model 530 Type All System containing Keithley Model 225 Current Source and Keithley Model 160 Digital Multimeter For the Micro Electronics Laboratory At University of Notre Dame Department of Electrical Engineering This user manual is not be removed from room 247A This includes making copies A downloaded copy can be obtained from the web at the following link http www nd edu ee ndnf or contact Keith Darr for a copy of this manual Purpose A Kulicke and Soffa Industries Inc Model 3007 four point in line probe is used in conjunction with a Keithley model 530 Type All system to make applicable characterization measurements The Keithley model 530 Type All system is an electronic system designed for measurement of resistivity and determination of conductivity type of a semiconductor The Keithley system contains a precision current source digital microvoltmeter in conjunction circuitry needed for resistivity and typing determinations Reference Documents Keithley model 530 instruction manual Keithley model 225 current source instruction manual Keithley model 160 digital multimeter instruction manual and Kulicke and Soffa Industries Inc model 3007 resistivity probe base instruction manual additional documentation has been cited at the end of this procedure Additional
7. Q current shunt resistor is selected Apply the current to the sample by switching the Type All system function selector to the current position dey elo S NOTE At times the limit light on the current source will be lit This is an indication that the probes have not made proper contact with the sample If this occurs place the Type All system and the current source back into their standby conditions and then release the locked chrome handle holding the probe against the sample Reposition the sample then lower and secure the chrome handle so to remake contact to the sample If the limit light is still lit after 3 reposition attempts contact lab staff 5 Read and record the voltage displayed on the voltmeter 1 Divide this voltage by the current value This resistance value should match the value of the current shunt resistor 1 Ifthe calculated value is equal to the current shunt resistor value then the current source is outputting the correct current value 2 Ifthe calculated value does not match the current shunt resistor value there is likely a problem with the four point probe and lab staff should be contacted Resistivity Measurement Maintaining the conditions as described above the sample resistivity V I can be easily determined This value in ohms is the resistivity of the sample at the point where the four point probe has been connected to the sample under test This value is a function of the position of the co
8. Standard Test Methods for Resistivity of Semiconductor Materials Instruction manual model 530 Type All system Keithley Instruments Oct 1974 Sheet resistance correction factors for circular and rectangular samples F M Smits Measurements of Sheet Resistivity with Four Point Probe Bell Syst Tech J 3 711 718 May 1958 Courtesy of AT amp T Bell Laboratories Anner George E Planar Processing Primer Van Nostrand Reinhold New York 1990 Haldor Topsoe Semiconductor Division Geometric Factors in Four Point Resistivity Measurement May 5 1966 pre revised edition May 25 1968 available for download at Bridge Technology s web site http www four point probes com haldor html Keith Darr 12 Rev 1 0 10 31 2008
9. ic contact by repositioning the sample in respect to the probe head This should be accomplished by placing the Type All system and current source back into standby releasing the probe head slightly reposition the sample and remaking contact by lowering and locking the chrome handle 1 In doing so the operator must perform the contact verification steps prior to re measurement of the V fwa and Vey values 2 Ifthe operator is unable to obtain resistance values that are within 10 of one another after multiple repositioning attempts contact lab staff Calculate the mean resistance V I Rrey Reya 2 and record this value as the spreading resistance Rsp 1 This value will be used to calculate the sheet resistance R and the slice resistance p Conductivity Type Procedure The four point probe can be used to determine the sample conductivity type through use of the AC signal rectification Another method is available to determine sample conductivity type when using the Type All system This method known as the thermoelectric mode or as the hot and cold probe method generates a voltage by means of the Seebeck effect to determine the carrier type 1 Set up the sample in the same manner as described in the contact verification procedure 2 Set the 530 Type All system to the type Rect function 1 Ifthe voltmeter indicates a value greater than 0 5 mV then the majority carrier type can be determined by the polarity indica
10. ions where a rectangular sample is being tested In that application the sheet resistance R will be calculated first and the slice resistance p will then be calculated as a function of the sheet resistance R p F R p R t R VD F F F t s t N Table 1 F t s Thickness correction factor as a function of the ratio of thickness to probe tip spacing If t s lt 0 5 then F t s 1 t s F t s 0 5 0 997 0 6 0 992 0 7 0 982 0 8 0 966 0 9 0 944 1 0 0 921 1 1 0 864 1 2 0 803 1 3 0 742 1 4 0 685 1 5 0 634 1 6 0 587 1 7 0 546 1 8 0 510 1 9 0 477 2 0 0 448 2 1 0 422 2 2 0 399 2 3 0 378 2 4 0 359 2 5 0 342 Q cm Q cm Q none cm cm cm Slice resistivity formula used for circular samples Slice resistivity formula used for rectangular samples The spreading resistance Geometric correction factor derived from table 1 for round samples Thickness of the sample expressed in cm Probe tip spacing expressed incm s 50mil 0 127 cm Sample diameter expressed in cm F Correction factor as a function of the ratio of probe tip spacing to sample diameter s d F 0 000 4 532 0 005 4 531 0 010 4 528 0 015 4 524 0 020 4 517 0 025 4 508 0 030 4 497 0 035 4 485 0 040 4 470 0 045 4 454 0 050 4 436 0 055 4 417 0 060 4 395 0 065 4 372 0 070 4 348 0 07
11. ling layer For example if the sample is a P type layer on top of an N type layer or an N type layer on top of a P type layer b Sizing requirements i Ifthe sample is round 1 The sample diameter must be greater than 150 mil 0 381 cm 3 s so to accommodate all four probe points ii Ifthe sample is rectangular 1 Sample length must be greater than 150 mil 0 381 cm 3 s so to accommodate all four probe points iii Geometric correction factors have only been included to compensate for round and rectangular samples 1 Corrections factors are needed to accurately calculated sheet and slice resistance of thin and of relatively small sized samples This is due to current source imaging that is created when the electron field comes into contact with an electrical boundary Keith Darr 5 Rev 1 0 10 31 2008 Equipment Setup 1 Check the logbook to make sure the last user has logged out 1 Read the log book comments of previous users to verify the machine condition 2 Log in to the log book 3 Ensure that the four point probe station is setup to the following stand by condition 1 The 163 digital voltmeter 1 Inthe 100 mV position 2 The LO and the HI banana plugs should have a shorting device connected to their respective plugs on both the 530 Type All system and the voltmeter 2 The 530 Type All system 1 Function set to standby 2 Power switch off 3 Probe set to the A position 4 Current shunt resistor set to 1K Q
12. ntacts on the sample surface and will differ if the operator were to test the sample at different points across the surface of the sample This resistivity measurement V I also referred to as the spreading resistance Rsp Should not be confused with other sample properties such as the sheet resistance R or the slice resistance p The technique for calculating the sheet resistance R and the slice resistance p are described latter in this procedure Keith Darr 7 Rev 1 0 10 31 2008 Resistivity Measurement 1 STON Se rh 9 Set the 530 Type All system to the Vwa function 1 Ensure that the output selector on the current source is in the position 2 Verify that the voltmeter is in the 100 mV position and that the current source is set to output a value of 1 00 mA left most mA position Record the value displayed on the voltmeter as V twa Divide this value by the selected current setting 1 to obtain the forward resistance Rgwa Change the 530 Type All system to the V rey function Change the output selector on the current source to the position Record the reading on the voltmeter as V pev Divide this value by the selected current setting I to obtain the reverse resistance Ryey The two readings Riwa and R ey should be within 10 of each other 1 Ifthe readings are different by a large value this is likely due to probe rectification 1 One may achieve a more ohm
13. ple is under test and the length a is less than 2 times the width d a lt 2d the sample approaches a circle in dimension Therefore the correction factor can be closely approximated by an estimation of the values that are between the curve for a circular sample and the defined rectangular sample in chart 1 Sheet resistance correction factors for circular and rectangular samples F M Smits Measurements of Sheet Resistivity with Four Point Probe Bell Syst Tech J 3 711 718 May 1958 Courtesy of AT amp T Bell Laboratories Keith Darr Rev 1 0 10 31 2008 10 Appendix Formulas and variables t s 50mil 0 127 cm d Viva Viev Riwa Vewa 1 Riev Viev L V z Riev HR iwa 2 R V D t s d s C p R t p F R F F F t s t F2 F t s R p t R C V D l w 1 mil 0 00254 cm Keith Darr Rev 1 0 10 31 2008 Units cm mil cm mA mA mV mV cm cm none Q cm Q cm none none none Q sq Q sq cm cm mil cm Description Sample thickness expressed in cm Probe tip spacing constant for this four point probe configuration Reverse current Forward current Forward voltage Reverse voltage Forward resistance Reverse resistance The average resistance as a function of the forward resistance Rgwq reverse resistance Rev The spreading resistance Rsp Ratio of the sample thickness
14. ted on the voltmeter 1 Positive polarity P type 2 Negative polarity N type 3 Ifthe reading is less than 0 5 mV then switch to the thermoelectric mode by selecting type Therm function 1 Ifthe voltmeter indicates a value greater than 0 5 mV then the majority carrier type can be determined by the polarity indicated on the voltmeter 1 Positive polarity P type 2 Negative polarity N type 4 If either of the two methods do not have desirable results 1 One may place the Type All system into the standby position release and reposition the sample in respect to the probe head remake contact and then perform the contact verification steps and the resistivity tests once more 5 Ifthe probe connection has been maintained and all tests have been completed return the Type All system and the current source to the standby condition 6 Release and remove the sample from the four point probe station 7 Turn off the current source voltmeter and the Type All system power 8 Complete the calculations of the sheet resistance Rs and the slice resistance p which are explained in the following sections 9 Clean up the work area enter needed comments in the log book and sign out of the log book Keith Darr 8 Rev 1 0 10 31 2008 Calculation of the sheet resistance R and the slice resistivity p Slice Resistivity p Slice resistance p expressed in units Q cm should be calculate before sheet resistance R except for situat
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