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1. ASTM F 1391 92 Method Carbon The thickness of reference wafer and test wafer are determined by either measuring the thickness using a caliper gauge or by calculating the thickness using the silicon phonon peak at 610cm in the absorbance spectra See section 3 1 The absorbance spectrum of the reference wafer is multiplied by the fac tor d d with d being the thickness of the test wafer and d being the thickness of the reference wafer The normalized absorbance spectrum of the reference wafer is sub tracted from the absorbance spectrum of the test wafer The maximum absorbance value of the carbon peak at 605cm is deter mined This data point plus two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parab ola The wavenumber of the parabola vertex Vmay and the corresponding absorption value Ap are determined On the basis of the spectrum calculated in step 3 a linear baseline is cal culated by fitting data points in the regions from 550 to 570cm and from 630 to 650cm using the least squares method The absorption value of the baseline Ag at the wavenumber Vmax is determined max The absorption coefficient for carbon a is calculated using the follow ing formula 23 03 4r de Oc with d being the thickness of the test wafer The carbon concentration cc is calculated by multiplying the absorption coefficient a by a calib
2. OPUS Spectroscopy Software User Manual Version 6 SEMI gt lt BRUKER de 2005 BRUKER OPTIK GmbH Rudolf Plank Str 27 D 76275 Ettlingen www brukeroptics com All rights reserved No part of this manual may be reproduced or transmitted in any form or by any means including printing photocopying microfilm electronic systems etc without our prior written per mission Brand names registered trademarks etc used in this manual even if not explicitly marked as such are not to be considered unprotected by trademarks law They are the property of their respective owner The following publication has been worked out with utmost care However Bruker Optik GmbH does not accept any liability for the correctness of the information Bruker Optik GmbH reserves the right to make changes to the products described in this manual without notice This manual is the original documentation for the OPUS spectroscopic software Table of Contents 1 UO a au EAEKO 1 2 Carbon Oxygen Analysis 1 eed eas hy cals ease eee LER es 2 241 Select Elles uo Dira t v EO oia Du a get pe quu Cod uu Y xard agat 3 2 2 Analysis Parameters zo que d Py aera D e E ae De ees 4 2 2 1 Oxygen Carbon Methods an ezne grek rregaz RT nn 4 2 2 2 Other Analysis Parameters arat SEN voe HR EN 6 2 3 Analysis RESUS gek A EE eX UA nUSIERQUM MENFE rot qd 7 3 Calculation Algorithms 0 cece ccc eee cece reece eens 8 3 1 Calculation of the
3. gt Display defa EZ Report Displ Figure 5 OPUS Report Window OifAfecmEI7 Cs Afecmet7 0 2359 9 12 0 02339 Analysis Results Bruker Optik GmbH OPUS SEMI 7 Calculation Algorithms 3 Calculation Algorithms This chapter describes the calculation algorithms of the different methods for determining the oxygen and the carbon impurity concentrations 3 1 Calculation of the Wafer Thickness For the calculation of the wafer thickness the silicon phonon peak at 610cm in the absorbance spectrum is used 1 The absorption values of the three data points at the wavenumbers 617 18 619 1 and 615 26cm are averaged The data point nearest to the specified wavenumber is chosen Note These data points are not exactly in the center of the peak but slightly off center 2 The baseline is a straight line calculated by fitting the six data points the data point at 651 Sem and the two neighboring data points as well as the data point at 576 68cm and the two neighboring data points using the least squares method 3 The y value of the baseline at 617 18cm is determined 4 This value is subtracted from the absorption value calculated in step 1 The result is called Ap 5 The wafer thickness is calculated using the following empirical formula d mm 0 02563 2 91474 Ap with 0 02563 being the default Offset value and 2 91474 being the default Slope value Note This formul
4. 9 The wavenumber of the parabola vertex vay and the corresponding absorption value Ap are determined On the basis of the spectrum calculated in step 3 a linear baseline is cal culated by fitting data points in the regions from 900 to 1000cm and from 1200 to 1300cm using the least squares method The absorption value of the baseline 4g at the wavenumber v is determined The transmittance values which correspond to the absorbance values Ap and Aj are calculated T 10 T510 10 The absorption coefficients ap and ag for the peak maximum and the baseline point are calculated using the following formula GEAN 0 09 i y 0 36 T e d 0 18 T with d being the thickness of the test wafer 11 The absorption coefficient for oxygen a is calculated Ao Ap AB 12 The oxygen concentration cg is calculated by multiplying the absorption coefficient a by a calibration factor IOC 88 co 3 14 10 cm ao This calibration factor is also called conversion coefficient The default value is 3 14 x leri This value can be changed by the user in the CARBon OXygen Analysis dialog window 13 The oxygen concentration value cg is multiplied by the factor FO default value FO 1 which can be specified by the user in the CARBon OXygen Analysis dialog window Co 7co FO Bruker Optik GmbH OPUS SEMI 15 Calculation Algorithms 3 8 1 2 3 4 5 6 7 8 9 10
5. absorption value of the reference wafer spectrum For the calculation of the so called ratio factor R the silicon peak at 738cm is used The y values of the data points at 740 6 738 0 and 736 0cm are averaged This average value ASIp is taken as intensity of the peak maximum For the calculation of the baseline five data points are used The absorp tion value of the left baseline point BL is the average value of the y values at the wavenumbers 1043 4 1041 5 and 1039 6cm The absorp tion value of the right baseline point BR is the average value of the y values at the wavenumbers 700 and 698cm The value the baseline ASIg at 73 8cm is calculated using the following formula uw BL 40 BR 300 340 The difference ASIp ASIp for both the test wafer spectrum and the reference wafer spectrum are calculated The results are ASI7 and ASIg The ratio factor R is calculated as follows _ ASTr AST n R The absorption value of carbon Ac is calculated using the following equation Ac Ar R An The carbon concentration c is calculated using the formula cc 7 10 14 cm e Ee 8 2 10 c D with Ap being the absorption value at 610cm silicon peak which has been calculated in the course of the thickness calculation for the test wafer spectrum See section 3 1 The factor 8 2 is the conversion coef ficient carbon which can be changed by the user in the CARBon OXy gen Analysis dialog wind
6. rough surface and or free charge carriers Note For the calculation algorithms of the available evaluation methods refer to chapter 3 The CARBon OXygen Analysis function of OPUS SEMI is suited for two types of wafers having different surface treatments Double side polished or polish etched wafers Single side polished wafers with etched back surfaces Bruker Optik GmbH OPUS SEMI Carbon Oxygen Analysis Carbon Oxygen Analysis Before starting a Carbon Oxygen Analysis acquire an absorbance spectrum of a pure silicon wafer produced by float zoning reference wafer and an absor bance spectrum of a silicon wafer containing Oi and Cs impurities test wafer that is to be analyzed Note When setting up the general measurement parameters define a resolution of 4 0 and a zerofilling factor of 2 After the measurement load the files containing the absorbance spectra refer ence and sample spectra into OPUS See figure 1 Test Wafer Spectrum Reference Wafer Spectrum Test Wafer Spectrum Reference Wafer Spectrum 1300 1200 1150 1100 1050 1000 950 900 850 800 750 700 650 600 550 Figure 1 Absorbance Spectra for the Carbon Oxygen Analysis 2 OPUS SEMI Bruker Optik GmbH Select Files 2 1 Select Files To determine the impurity concentrations of interstitial oxygen Oi and substi tutional carbon Cs in a silicon wafer select in the OPUS Evaluate menu the CARBon OXygen A
7. 5 S Single side polished wafer 1 19 Slope 6 8 Substitutional carbon 1 3 5 26 28 T Two sided polished test pieces 28 W Wafer thickness 1 3 5 8 12 13
8. 3 1 Note First the carbon absorption coefficients are calculated separately for test wafer spectrum and reference wafer spectrum 2 3 4 3 6 The data point at 605 6cm and two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parabola The y value of the parabola Ap at the wavenumber 605 6cm is deter mined A linear baseline is calculated by fitting six data points the data point at 622 97cm and the two neighboring data points as well as the data point at 567 04cmr and the two neighboring data points using the least squares method The y value of the baseline Ap at 605 6cm is determined The absorption coefficients a for Ap and Ap are calculated using the fol lowing formula 1 TUR O R 4T R n d 2T R with d being the wafer thickness R ratio factor having the value 0 3 and T 10 Bruker Optik GmbH OPUS SEMI 13 Calculation Algorithms 3 7 7 8 9 10 1 2 3 4 5 The absorption coefficient calculated for the baseline point is subtracted from the absorption coefficient calculated for the peak at 605cm Op Gg The results are net absorption coefficients for the test wafer and the reference wafer ar and ap To calculate the absorption coefficient for carbon a the net absorp tion coefficient of the test wafer is subtracted from the net absorption coef
9. 391 92 Standard Test Method for Substitutional Atomic Carbon Content of Sili con by Infrared Absorption 1 Scope 1 1 This referee test method covers the determination of substitutional carbon concentration in single crystal silicon Because carbon may also reside in inter stitial lattice positions when in concentrations near the solid solubility limit the result of this test method may not be a measure of the total carbon concentra tion 1 2 The useful range of carbon concentration measurable by this test method is from the maximum amount of substitutional carbon soluble in silicon down to about 0 1 parts per million atomic ppma that is 5 x 10P cm for measure ments at room temperature and down to about 0 01 ppma that is 0 5 x 10 5 cm at cryogenic temperatures below 80 K 1 3 This test method utilizes the relationship between carbon concentration and the absorption coefficient of the infrared absorption band associated with sub stitutional carbon in silicon At room temperatures about 300 K the absorp tion band peak is at 605cm or 16 53 um At cryogenic temperatures below 80 K the absorption band peak is at 607 5cm or 16 46um 1 4 This test method is applicable to slices of silicon with a resistivity higher than 3Q cm for p type and higher than 1Q cm for n type Slices an be any crys tallographic orientation and should be polished on both surfaces 1 5 This method is intended to be used infrared spectrophotomete
10. Analysis dialog window Gar co FO Bruker Optik GmbH OPUS SEMI 21 Calculation Algorithms 3 11 1 2 3 4 5 DIN 50438 2 82 Method Carbon The thickness of reference wafer and test wafer are determined by either measuring the thickness using a caliper gauge or by calculating the thickness using the silicon phonon peak at 610cm in the absorbance spectra See section 3 1 The absorbance spectrum of the reference wafer is multiplied by the fac tor d d with d being the thickness of the test wafer and d being the thickness of the reference wafer The absorbance spectra are converted into transmittance spectra Tr 10755 A so called comparison spectrum is calculated by dividing the test wafer spectrum by the reference wafer spectrum The minimum transmittance value of the carbon peak at 605cm is determined provided that the spectrum has been acquired at room tem perature Note In case the spectrum has been acquired at cryogenic temperatures the min imum transmittance value of the carbon peak at 607 5cm is determined 6 7 8 9 10 11 This data point plus two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parab ola The wavenumber of the parabola vertex vpi transmittance value Ty are determined and the corresponding The baseline is constructed as a tangent to the comparison spect
11. Oxygen ASTM F 1391 92 Carbon DIN 50438 1 A 93 Oxygen DIN 50438 1 B 93 Carbon DIN 50438 2 82 Carbon It is highly recommended to purchase these standards You can order them for example at the Beuth Verlag GmbH www beuth de or at ASTM International www astm org This appendix quotes the scope or range of application and purpose of the following standards e ASTMF 1188 93a e ASTM F 1391 92 DIN 50438 1 DIN 50438 2 82 ASTM F 1188 933 Standard Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption 1 Scope 1 1 This test method covers the determination of the interstitial oxygen content of single crystal silicon by infrared spectroscopy This test method requires the use of an oxygen free reference specimen 1 2 The useful range of oxygen concentration measurable by this test method is from 1 x 10 atoms cm to the maximum amount of interstitial oxygen soluble in silicon 1 3 The oxygen concentration obtained using this test method assumes a linear relationship between the interstitial oxygen concentration and the absorption coefficient of the 1 107cm band associated with interstitial oxygen in silicon 14 1 ASTM F 1188 93a Published 1993 Standard Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption ASTM International West Conshohocken Pennsylvania U S Bruker Optik GmbH OPUS SEMI 25 Appendix ASTM F 1
12. Wafer bizker 8 3 2 Ratio Method SAO VBefl os ag ada TRE EST EE a rai 9 3 3 Ratio 2 Method Oxygen uses mew RR RESAP ra E WS ag 10 3 4 Ratio Method erla EAEKO 10 3 5 Pseudo ASTM Method Oxygen AAA 12 3 6 Pseudo ASTM Method GORO 13 3 7 ASTM F 1188 93a Method Oxygen rrura sos ia ibarrez xx nS 14 3 8 ASTM F 1391 92 Method Carbon assa 16 3 9 DIN 50438 1 A 93 Method Oxygen usus 17 3 10 DIN 50438 1 ERNE BRISKA GE 19 3 11 DIN 50438 2 82 Method Carbon s z 22 1 Introduction The software package OPUS SEMI is intended for analyses in the field of semi conductor quality control On the basis of an absorbance spectrum of a wafer this OUS function calculates the impurity concentration of interstitial oxygen Oi and substitutional carbon Cs in silicon wafers OPUS SEMI provides evaluation methods based on the following ASTM and DIN standards e ASTM F 1188 93a Oxygen e ASTM F 1391 92 Carbon DIN 50438 1 A 93 Oxygen DIN 50438 1 B 93 Oxygen DIN 50438 2 82 Carbon Besides the evaluation methods based on the above listed ASTM and DIN stan dards the following methods are available The pseudo ASTM method which requires that the wafer thickness is already known The ratio method which automatically computes the wafer thickness from the silicon matrix peaks A special ratio method which is designed to deal with strongly curved baselines which can occur when analyzing samples with a
13. a can only be used for double side polished wafers having a certain thickness range approx from 0 3 to 2 5mm For a more flexible thickness calculation the parameters Offset a and Slope b in the above formula are free parameters d mm a be 4p 8 OPUS SEMI Bruker Optik GmbH Ratio 1 Method Oxygen 3 2 1 2 3 4 5 6 7 8 9 10 Ratio 1 Method Oxygen The data point at 1107 08cm and two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parabola The y value of this parabola Ap at the wavenumber 1107 08cmr is determined A linear baseline is calculated by fitting six data points the data point at 1299 9cm and two neighboring data points as well as the data point at 940cm and two neighboring data points using the least squares method The y value of the baseline Ag at 1107 08cm is determined The difference der de for both the test wafer spectrum and the refer ence wafer spectrum are calculated The results are Ay absorption value of the test wafer spectrum and Ap absorption value of the reference wafer spectrum For the calculation of the so called ratio factor R the silicon peak at 738cm is used The y values of the data points at 740 6 738 0 and 736 0cm are averaged The calculated average value ASIp is taken as intensity of the peak maximum For the calculation of the baseline fi
14. and the height of the carbon peak at 605cm are calcu lated for both spectra 1 e the reference wafer spectrum and the test wafer spec trum For this purpose proper baselines are fitted Then a so called ratio factor is calculated using the silicon peak at 738enr The oxygen and carbon peak heights of reference wafer spectrum are multiplied with this ratio factor and subtracted from the peak height of the test wafer spectrum Using the corrected peak heights the software calculates the oxygen and carbon concentrations by dividing these peak heights by the height of the baseline corrected silicon peak at 617cm of the test wafer spectrum and multiplying it by appropriate propor tional factors In case of RATIO Method 1 linear baselines are fitted whereas in case of RATIO Method 2 a quadratic polynomial is used for the oxygen baseline This method can be used for spectra with a strong curved baseline The Pseudo ASTM Method can only be used for silicon slices polished on both sides Taking the multiple reflections on both wafer surfaces into account the formula for calculating the transmittance spectrum T 10 bsorbance jg Ge 1 R e 1 pase with d being the wafer thickness and R being the reflectivity 0 3 Using the this formula the absorption coefficient a is calculated The a values for the peak and the baseline point are evaluated and then the baseline value is subtracted from the peak value This is done for both the
15. by dividing the test wafer spectrum by the reference wafer spectrum The minimum transmittance value of the oxygen peak at 1107emrl is determined This data point plus two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parab ola The wavenumber of the parabola vertex Vin and the corresponding transmittance value Ty are determined n On the basis of the spectrum calculated in step 4 a linear baseline is cal culated by fitting data points in the regions from 1025 to 1040cm and from 1180 to 1195cm using the least squares method The transmittance value of the baseline Tg at the wavenumber ita is determined min The absorption coefficient for oxygen dg is calculated using the follow ing formula Bruker Optik GmbH OPUS SEMI 17 Calculation Algorithms ao _ In A V4 B d with A 42 1 8 27 M oes ad R p Q Qt 477 Qt phon AN 1 Q phon 0 85 cm D Si ay 1 43 10 cm N p n Si eurie 10 cm N n with N n and N p being the free charge carrier concentrations for p and n type silicon 11 The oxygen concentration cg is calculated by multiplying the absorption coefficient a by a calibration factor co 3 14 10 cm ao This calibration factor is also called conversion coefficient The default value is 3 14 x 10 7cm This value can be changed by the user in the CARBon OXygen Analysis dialog wi
16. ectrum T the values Ty and Tp are calculated as fol lows 14 The minimum transmittance value of the oxygen peak at 1107emrl is determined 15 This data point plus two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parab ola 16 The wavenumber of the parabola vertex v i intensity value Ty are determined and the corresponding 17 A linear baseline is calculated by fitting data points in the regions from 1025 to 1040cmr and from 1180 to 1195cm using the least squares method 18 The transmittance value of the baseline Tg at the wavenumber Vin is determined 20 OPUS SEMI Bruker Optik GmbH DIN 50438 1 B 93 Method Oxygen 19 The absorption coefficient for oxygen ag is calculated using the follow ing formula ao _ In 4 4 B d with A SE 1B M 1 dek BOA with ag being the absorption coefficient which has been calculated in step 13 and d being the thickness of the test wafer 20 The oxygen concentration is calculated by multiplying the absorption coefficient co by the calibration factor co 3 14 10 cm ao This calibration factor is also called conversion coefficient The default value is 3 14 x 10 7cm This value can be changed by the user in the CARBon OXygen Analysis dialog window 21 The oxygen concentration value is multiplied by the factor FO which can be specified by the user in the CARBon OXygen
17. esults double click on the Quant data block As a result the OPUS report window opens Depending on the number of analyses e g using different methods you have performed there are several carbon oxygen analysis reports displayed in form of a directory tree Clicking on one of them displays the corresponding analysis result Quant Data Block Carbon Oxygen Analysis Reports aE File Edit view Window Measure Manipulate Evaluate Display Print Macro Validation Setup Help ESS Je Keres JAT lames joN c ie EE 1x lm mmm e Ma Display default p BlmiReport Displa dazaz Oper af sit_1 0 E M Doku MAFFEI Data parame PUS 6 0 SEMI Ausgang 4 Method RATIO Method 2 CC Oxygen E17 cm 344 CC Carbon E17 cm2 0 82 FO 1 EG 1 EZ Reference Wafer 0 40G_Ettlingen SDAE Messdaten e SE Si_Reference 0 1 EH 5 se 3c c jusronv Carbon Oxygen Analysis Report Carbon Oxygen Analysis Report Carbon Oxygen Analysis Report Carbon Oxygen Analysis Report Carbon Oxygen Analysis Report Used Analysis Parameters Data parameters Sc5m ScRF Data parameters ScRF Sample Parameters Optic Parameters Acquisition parameters FT Parameters Instrument parameters Datafile History E MADokulMAFEYOPUS 6 0 SEMI Ausgang Data parameters AB AB Data parameters Sc5m ScSm ScRF Data parameters ScRF Acquisition parameters FT Parameters Optic Parameters X E
18. ficient of the reference wafer Ac ATAR The carbon concentration cc is calculated by multiplying the absorption coefficient ac by a calibration factor cc 8 29 I0 cm ac This calibration factor is also called conversion coefficient The default value is 8 2 x 10 6cm This value can be changed by the user in the CARBon OXygen Analysis dialog window The carbon concentration value c calculated in step 9 is multiplied by the factor FC default value FC 1 which can be specified in the CAR Bon OXygen Analysis dialog window Ger gen FC ASTM E 1188 93a Method Oxygen The thickness of reference wafer and test wafer are determined by either measuring the thickness using a caliper gauge or by calculating the thickness using the silicon phonon peak at 610cm in the absorbance spectra See section 3 1 The absorbance spectrum of the reference wafer is multiplied by the fac tor d d with d being the thickness of the test wafer and d being the thickness of the reference wafer The normalized absorbance spectrum of the reference wafer is sub tracted from the absorbance spectrum of the test wafer The maximum absorbance value of the oxygen peak at 1107emr is determined This data point plus two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parab ola 14 OPUS SEMI Bruker Optik GmbH ASTM E 1188 93a Method Oxygen 6 7 8
19. fol lowing formula m gc Rt RT R d 2T R with d being the wafer thickness R ratio factor having the value 0 3 and T 10 The absorption coefficient calculated for the baseline point is subtracted from the absorption coefficient calculated for the peak at 1107cm ap ag The results are net absorption coefficients for the test wafer and the reference wafer ar and ap To calculate the absorption coefficient for oxygen a the net absorption coefficient of the test wafer is subtracted from the net absorption coeffi cient of the reference wafer Qo ATOR 12 OPUS SEMI Bruker Optik GmbH Pseudo ASTM Method Carbon 9 10 3 6 1 The oxygen concentration Cg is calculated by multiplying the absorption coefficient a by a calibration factor co 3 14 10 cm ao This calibration factor is also called conversion coefficient The default value is 3 14 x 10 cm This value can be changed by the user in the CARBon OXygen Analysis dialog window The oxygen concentration value co calculated in step 9 is multiplied by the factor FO default value FO 1 which can be specified by the user in the CARBon OXygen Analysis dialog window Gar co FO Pseudo ASTM Method Carbon The thickness of reference wafer and test wafer are determined by either measuring the thickness using a caliper gauge or by calculating the thickness using the silicon phonon peak at 610cm in the absorbance spectra See section
20. following dialog window appears CARBon OXygen Analysis X Select Files Analysis Parameters Oxygen Carbon method Units ASTM F 1188 93a ASTM F 1331 32 z f ppm atomic C Atoms ccm r Conversion coefficients Oxygen 314 Elz cm Carbon 0 82 E17 cm Thickness calculation 5 Factors Offset 0 02563 Factor FO 1 b Slope 2 91474 Factor FC 1 Analyze Cancel Help Figure 3 Carbon Oxygen Analysis Dialog Window Analysis Parameters 2 2 1 Oxygen Carbon Methods In this dialog window you specify the parameters for the carbon oxygen analy sis The following evaluation methods are available ASTM F 1188 93a ASTM F 1391 92 DIN 50438 1 A 93 ASTM F 1391 92 DIN 50438 1 B 93 ASTM F 1391 92 RATIO Method 1 RATIO Method 2 Pseudo ASTM No Oxygen Analysis DIN 50438 2 82 The methods for calculating the interstitial oxygen concentration are e ASTMF 1188 93a DIN 50438 1 A 93 DIN 50438 1 B 93 RATIO Method 1 RATIO Method 2 Pseudo ASTM 4 OPUS SEMI Bruker Optik GmbH Analysis Parameters The methods for calculating the substitutional carbon concentration are e ASTM F 1391 92 e RATIO Method Pseudo ASTM DIN 50438 2 82 The RATIO Methods 1 and 2 are suited for double side polished wafers and for wafers with a rough backside Using these methods the height of the oxygen peak at 1107cm
21. ilicon peak at 610cm has an influence on the oxygen concentration calculation Ratio 2 Method Oxygen The difference between Ratio 1 Method and Ratio 2 Method concerns only step 3 For determining the absorption value of the baseline Ap a parabola is fitted A parabolic baseline is calculated by fitting the following 12 data points 3 4 data point at 1299 9cm and the two neighboring data points data point at 1180cm and the two neighboring data points data point at 1040cnr and the two neighboring data points data point at 940cnr and the two neighboring data points Ratio Method Carbon 1 The data point at 605 6cm and two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parabola 2 The y value of the parabola Ap at the wavenumber 605 6cm is deter mined 3 Alinear baseline is calculated by fitting six data points the data point at 622 97cm and the two neighboring data points as well as the data point at 567 04cmr and the two neighboring data points using the least square method 4 The y value of the baseline Ag at 605 6cm is determined 10 OPUS SEMI Bruker Optik GmbH Ratio Method Carbon 5 6 7 8 9 10 11 The difference der 45 for both the test wafer spectrum and the refer ence wafer spectrum are calculated The results are Ay absorption value of the test wafer spectrum and Ap
22. lt parameters are only valid for double side polished wafers and a cer tain thickness range approx from 0 3 to 2 5mm If your wafer does not fulfill the above mentioned conditions concering surface treatment and thickness you need to change these default values Note It is better to work with known thickness values than to calculate them on the basis of the FT IR spectrum as described in chapter 3 section 3 1 In case of the method DIN 50438 1 A 93 the concentration of the free charge carriers needs to be entered as well See figure 4 CARBon OXygen Analysis X Select Files Analysis Parameters c0 ppm atomic DIN 50438 1 A 33 ASTM F 1391 92 s m Oxygen Carbon method r Units C Atoms ccm Conversion coefficients Charge carrier concentration T psi Parameters of the EZE 314 EI diz E ederki Charge Carrier C nsi Carbon 9 82 E1 cm Concentration r Thickness calculation Factors Offset 0 02563 Factor FO 1 Sa Slope 2 91474 Factor FC 1 Analyze Cancel Help Figure 4 Analysis Parameters of the Charge Carrier Concentration 6 OPUS SEMI Bruker Optik GmbH Analysis Results 2 3 Analysis Results After having entered all analysis parameters click on the Analyze button See figure 4 The results of a carbon oxygen analysis are stored in a Quant data block figure 5 which is attached to the test wafer spectrum file To display the analysis r
23. n Transmissionsgrad 8 15 L D kalzi 1 f 1300 1200 1100 1000 cm 900 Wellenzahl v Figure 6 Leveling the Spectrum of a single side polished Test Wafer Source DIN 50438 1 Pr fung von Materialien f r die Halbleitertechnologie Bestimmung des Verunreinigungsgehaltes in Silicium mittels Infrarot Absorption Teil 1 Berlin Beuth Verlag GmbH 1995 07 Bruker Optik GmbH OPUS SEMI 19 Calculation Algorithms 8 isthe transmittance value at 1188cm of the leveled spectrum See curve c in figure 6 After that the adjusted transmittance spectrum of the reference wafer is calcu lated as follows 9 The transmittance value O at 1188cm in the reference spectrum 1s determined This value has been corrected for thickness step 2 and 3 10 This spectrum is multiplied by the factor The result is an adjusted transmittance spectrum 11 Op is the transmittance value at 1107cnr This value is required for the calculation of absorption coefficient ag See step 13 12 The leveled test wafer spectrum curve c in figure 6 is divided by the adjusted reference wafer spectrum to obtain the comparison spectrum T 13 The absorption coefficient a is calculated using the following formula CB In Dt 4D 1 111 d with d being the thickness of the test wafer The parameter D is calcu lated as follows 22722 Or D Using the comparison sp
24. nalysis function The following dialog window appears CARBon OXygen Analysis 1 x Select Files Analysis Parameters r Reference wafer spectrum r File s for CARBOX analysis Known thickness Reference wafer 0 mm Test wafer 0 mm Analyze Cancel Help Figure 2 Carbon Oxygen Analysis Dialog Window Select Files Drag and drop the absorbance data block of the reference wafer in the upper field Reference wafer spectrum and the absorbance data block s of the test wafer s in the lower field File s for CARBOX analysis Note The OPUS function CARBon OXygen Analysis accepts only absorbance data blocks Note This OPUS function allows also the evaluation of a 3D data block of the test wafer In this case the concentrations O and C are displayed as traces Enter the thickness values in mm of the reference and the test wafer in the cor responding fields provided that these values are known For all evaluation methods except for RATIO Method 1 and RATIO Method 2 the thickness val ues of the reference and the test wafer need to be entered If the thickness is unknown enter the value 0 In this case the thickness is calculated using the sil icon phonon peak at 610cm The algorithm for the wafer thickness calcula tion is described in detail in chapter 3 Bruker Optik GmbH OPUS SEMI 3 Carbon Oxygen Analysis 2 2 Analysis Parameters Click on the Analysis Parameter tab The
25. ndow 12 The concentration value cg is multiplied by the factor FO which can be specified by the user in the CARBon OXygen Analysis dialog window Gar co FO 18 OPUS SEMI Bruker Optik GmbH DIN 50438 1 B 93 Method Oxygen 3 10 1 2 3 DIN 50438 1 B 93 Method Oxygen The thickness of reference wafer and test wafer are determined by either measuring the thickness using a caliper gauge or by calculating the thickness using the silicon phonon peak at 610cm in the absorbance spectra See section 3 1 The absorbance spectrum of the reference wafer is multiplied by the fac tor d d with d being the thickness of the test wafer and d being the thickness of the reference wafer The absorbance spectra are converted into transmittance spectra Tr 10755 After that the leveled transmittance spectrum of the test wafer is calculated as follows 4 5 6 7 is the transmittance value at 1107cm of curve a in figure 6 This spectrum curve a in figure 6 is leveled linearly in such a way that the transmittances values at the wavenumbers 1200cmr and 1025cm are identical See curve b in figure 6 O is the transmittance value at 1107cnr of the linearly leveled spec trum See curve b in figure 6 The linearly leveled spectrum curve b in figure 6 is multiplied by O The result is the leveled spectrum See curve c in figure 6 Xr L bl Mefiprobenspektrum N
26. ow The carbon concentration value is multiplied by the factor FC which can be specified by the user Gar gen FC Bruker Optik GmbH OPUS SEMI 11 Calculation Algorithms 3 5 Note The thickness value is not used for the oxygen concentration calculation Only the baseline corrected absorbance value Ap of the silicon peak at 610cm has an influence on the oxygen concentration calculation 1 Pseudo ASTM Method Oxygen The thickness of reference wafer and test wafer are determined by either measuring the thickness using a caliper gauge or calculating the thick ness using the silicon phonon peak at 610cm in the absorbance spectra See section 3 1 Note First the oxygen absorption coefficients are calculated separately for test wafer spectrum and reference wafer spectrum 2 3 4 3 6 7 8 The data point at 1107 08cm and two data points on the right and two data points on the left totally 5 data points are used for a least squares fit to a parabola The y value of this parabola Ap at the wavenumber 1107 08cmr is determined A linear baseline is calculated by fitting six data points the data point at 1299 9cm and the two neighboring data points as well as the data point at 940cm and the two neighboring data points using the least squares method The y value of the baseline Ag at 1107 08cm is determined The absorption coefficients a for Ap and Ag are calculated using the
27. ration factor cc 8 2 10 em ac This calibration factor is also called conversion coefficient The default value is 8 2 x 10 6cm This value can be changed by the user in the CARBon OXygen Analysis dialog window 16 OPUS SEMI Bruker Optik GmbH DIN 50438 1 A 93 Method Oxygen Note The conversion coefficient 0 82 x 10 7cm is valid for spectra acquired at room temperature But this method can also be used for spectra acquired at cryogenic temperatures below 80 K In this case the absorption band peak is at 607 5cm and the recommended conversion coefficient is 0 37 x 10 cm 11 3 9 1 2 3 4 5 6 7 8 9 10 2 The carbon concentration value c is multiplied by the factor FC default value FC 1 which can be specified by the user in the CARBon OXygen Analysis dialog window Cc 7cc FC DIN 50438 1 A 93 Method Oxygen The thickness of reference wafer and test wafer are determined by either measuring the thickness using a caliper gauge or by calculating the thickness using the silicon phonon peak at 610enr in the absorbance spectra See section 3 1 The absorbance spectrum of the reference wafer is multiplied by the fac tor d d with d being the thickness of the test wafer and d being the thickness of the reference wafer The absorbance spectra are converted into transmittance spectra Tr 107 bs A so called comparison spectrum is calculated
28. rdless of conductivity type and crystal orientation The measurement range for the carbon concentration lies between 5 x 10 cm and about 3 x Ilten Due to the strong silicon lattice absorption absorption coefficient Kg Seri for wave number 605 cm 2 that is superimposed on the 605cm band generated by the carbon the carbon content can only be determined using a dif ferential process 1 DIN 50438 Part 2 1982 Testing of Materials for Semiconductor Technology Determination of Im purity Content in Silicon Using Infrared Absorption Carbon Berlin Beuth Verlag GmbH 28 OPUS SEMI Bruker Optik GmbH Index A Absorption coefficient 5 6 12 13 14 15 17 18 20 21 22 25 26 28 ASTM F 1188 93a 1 4 5 14 25 ASTM F 1391 92 1 4 5 16 25 26 C Calibration factor 13 14 15 16 18 21 22 23 Charge carrier concentration 6 18 28 Conversion coefficient 6 10 11 13 14 15 16 17 18 21 23 D DIN 50438 1 2 27 DIN 50438 1 A 93 1 4 6 17 DIN 50438 1 B 93 1 4 19 DIN 50438 2 1 4 22 25 28 Double side polished wafer 1 5 27 F FC factor 6 11 14 17 23 FO factor 6 10 13 15 18 21 I Interstitial oxygen 1 3 4 25 27 O Offset 6 8 One side polished wafer 27 P Polish etched wafer 1 27 Pseudo ASTM method 1 4 5 12 13 Q Quant data block 7 Quant report 6 R Ratio 1 method 9 Ratio 2 method 10 Ratio factor 5 9 11 12 13 Ratio method 1 4
29. refer ence wafer spectrum and the test wafer spectrum Then the a values from the reference measurement are subtracted from those of the test wafer spectrum These corrected a values are proportional to the impurity concentrations Note The complete calculation algorithms for all evaluation methods are described in chapter 3 If you are not sure which oxygen carbon method you should use select ASTM F 1188 93a oxygen and ASTM F 1391 92 carbon Bruker Optik GmbH OPUS SEMI 5 Carbon Oxygen Analysis 2 2 2 Other Analysis Parameters In the group field Units specify the unit ppm atomic or atoms ccm in which the concentration values in the Quant report are to be displayed by clicking on the corresponding option button In the group field Conversion Coefficients specify the conversion coefficients for oxygen and carbon These conversion coefficients are multiplied by the absorption coefficients for the oxygen peak and the carbon peak to get the con centration values For the evaluation methods based on ASTM standards the default values of the conversion coefficients are oxygen 3 14 E17 cm and car bon 0 82 E17 cm The multiplication factors Factor FO oxygen and Factor FC carbon have the default value 1 If you measure calibration wafers with known oxygen and carbon concentrations you can use these factors for your calibration In the group field Thickness Calculation you specify the Offset and the Slope The defau
30. rs that operate in the region from 2000 to 500cm 5 20um 1 6 This test method provides procedure and calculation sections for the cases where the thickness values of test and reference specimens are both closely matched and not closely matched 1 7 1 ASTM F 1391 92 Published 1992 Standard Test Method for Substitutional Atomic Carbon Content of Silicon by Infrared Absorption ASTM International West Conshohocken Pennsylvania U S 26 OPUS SEMI Bruker Optik GmbH DIN 50438 Part 1 Testing of Materials for Semiconductor Technology Determination of Impurity Content in Semiconductors by Infrared Absorption Part 1 Oxygen 1 Range of Application and Purpose The Methods A and B of this standard serve to determine with high precision the oxygen content of silicon by non destructive optical infrared means Only the interstitial oxygen content of the silicon is detected by these methods The total oxygen content may be greater than the interstitial oxygen content The range of application of the methods is limited to plane parallel mono or polycrystalline silicon wafers with thicknesses d gt 0 03 cm and charged carrier concentrations N lt 2x10 cm and is independent of crystal orientation The methods are applicable to both of the currently used types of specimens having different surface treatments and thicknesses Double side polished or polish etched wafers with a thickness d 0 006 cm Me
31. rum in such a way that the spectrum contacts it at least at one point on each side of the absorption band but it is not cut at any point The transmittance value of the baseline Tg at the wavenumber Vmin is determined The absorption coefficient for carbon a is calculated using the follow ing formula GE In T3 Tu E d The carbon concentration c is calculated by multiplying the absorption coefficient ac by a calibration factor eur 1 09 10 cm ac 22 OPUS SEMI Bruker Optik GmbH DIN 50438 2 82 Method Carbon This calibration factor is also called conversion coefficient The default value is 1 0 x Oierri This value can be changed by the user in the CARBon OXygen Analysis dialog window Note The conversion coefficient 1 0 x 10 cm is valid for spectra acquired at room temperature But this method can also be used for spectra acquired at cryo genic temperatures below 80 K In this case the absorption band peak is at 607 5cm and the recommended conversion coefficient is 0 45 x 10 cm 12 The concentration value c is multiplied by the factor FC which can be specified by the user in the CARBon OXygen Analysis dialog window Cou erc Bruker Optik GmbH OPUS SEMI 23 Calculation Algorithms 24 OPUS SEMI Bruker Optik GmbH Appendix ASTM and DIN Standards As already mentioned in chapter 1 the OPUS SEMI software supports the fol lowing ASTM and DIN standards e ASTM F 1188 93a
32. thod A e One side polished wafers with etched back surfaces and thicknesses d 2 0 003 cm Method B Specimens having only sawed or only lapped surfaces do not fulfill the require ments of this standard The measurement range for oxygen concentration lies between 047525 X 10P cm and the solubility of oxygen of about 2 5 x 10 5cm at the melting point of silicon 1 DIN 50438 Part 1 1993 Testing of Materials for Semiconductor Technology Determination of Impu rity Content in Semiconductors by Infrared Absorption Oxygen in Silicon Berlin Beuth Verlag GmbH Bruker Optik GmbH OPUS SEMI 27 Appendix DIN 50438 Part 21 Testing Materials for Semiconductor Technology Determination of Impu rity Content in Silicon Using Infrared Absorption Part 2 Carbon 1 Range of Application and Purpose The process according to this standard is used to determine the carbon content of silicon The absorption coefficient of substitutional carbon at a wave number of 605 cm 16 5 um absorption band is used to measure carbon content Therefore this procedure does not apply to carbon that may be present in another form in the silicon lattice or chemically linked or is precipitated at gain boundaries or other places With this limitation the application range of the procedure covers plane parallel two sided polished test pieces of single crystal or polycrystalline silicon with charge carrier concentrations under 5 x 10cm rega
33. ve data points are used The absorp tion value of the left baseline point BL is the mean value of the y val ues at 1043 4 1041 5 and 1039 6cm The absorption value of the right baseline point BR is the mean value of the y values at 700 and 698cm The value of the baseline ASIp at 738 cm is calculated using the following formula m BL 40 BR e 300 340 The difference ASIp AST for both the test wafer and the reference wafer spectrum are calculated The results are ASI and ASIg The ratio factor R is calculated as follows R ASI r ASIR The absorption value of oxygen A is calculated using the following equation Ao Ar R An Bruker Optik GmbH OPUS SEMI 9 Calculation Algorithms 3 3 11 The oxygen concentration c is calculated using the following formula co 6 4 cm e 4o 3 140 10 cm Ap with Ap being the absorption value at 610enr silicon peak which has been calculated in the course of the thickness calculation for the test wafer spectrum See section 3 1 The factor 3 4 is the conversion coef ficient oxygen which can be changed by the user in the CARBon OXy gen Analysis dialog window 12 Then the calculated oxygen concentration value is multiplied by the factor FO Factor Oxygen which can be specified by the user Co co FO Note The thickness value is not used for the oxygen concentration calculation Only the baseline corrected absorption value Ap of the s

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