1、Designation: F1894 98 (Reapproved 2011)Test Method forQuantifying Tungsten Silicide Semiconductor Process Filmsfor Composition and Thickness1This standard is issued under the fixed designation F1894; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the quantitative determinationof tungsten and silicon concentrati
3、ons in tungsten/silicon(WSix) semiconductor process films using Rutherford Back-scattering Spectrometry (RBS).2(1) This test method alsocovers the detection and quantification of impurities in themass range from phosphorus (31 atomic mass units (amu) toantimony (122 amu).1.2 This test method can be
4、used for tungsten silicide filmsprepared by any deposition or annealing processes, or both.The film must be a uniform film with an areal coverage greaterthan the incident ion beam (;2.5 mm).1.3 This test method accurately measures the following filmproperties: silicon/tungsten ratio and variations w
5、ith depth,tungsten depth profile throughout film, WSixfilm thickness,argon concentrations (if present), presence of oxide on surfaceof WSixfilms, and transition metal impurities to detectionlimits of 131014atoms/cm2.1.4 This test method can detect absolute differences insilicon and tungsten concentr
6、ations of 63 and 61 atomicpercent, respectively, measured from different samples inseparate analyses. Relative variations in the tungsten concen-tration in depth can be detected to 60.2 atomic percent with adepth resolution of 670.1.5 This test method supports and assists in qualifying WSixfilms by
7、electrical resistivity techniques.1.6 This test method can be performed for WSixfilmsdeposited on conducting or insulating substrates.1.7 This test method is useful for WSixfilms between 20 and400 nm with an areal coverage of greater than 1 by 1 mm2.1.8 This test method is non-destructive to the fil
8、m to theextent of sputtering.1.9 A statistical process control (SPC) of WSixfilms hasbeen monitored since 1993 with reproducibility to 64%.1.10 This test method produces accurate film thicknesses bymodeling the film density of the WSixfilm as WSi2(hexagonal)plus excess elemental Si2. The measured fi
9、lm thickness is alower limit to the actual film thickness with an accuracy lessthan 10 % compared to SEM cross-section measurements (see13.4).1.11 This test method can be used to analyze films on wholewafers up to 300 mm without breaking the wafers. The sitesthat can be analyzed may be restricted to
10、 concentric rings nearthe wafer edges for 200-mm and 300-mm wafers, dependingon system capabilities.1.12 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.13 This standard does not purport to address all of thesafety concerns, i
11、f any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. The reader isreferenced to Section 8 of this test method for references tosome of the re
12、gulatory, radiation, and safety considerationsinvolved with accelerator operation.2. Referenced Documents2.1 Terminology used in this document is consistent withterms and definitions as used in the Compilation of ASTMStandard Definitions,8thed ASTM, 1994, Philadelphia PA,USA, specifically for terms
13、taken from the following ASTMstandards:2.2 ASTM Standards:3E135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE673 Terminology Relating to Surface AnalysisE1241 Guide for Conducting Early Life-Stage ToxicityTests with Fishes3. Terminology3.1 Numerous terms specif
14、ic to RBS and ion stopping insolids can be found in the following references (1, 2)2.3.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction of Committee F01 on Electronics ,andis the direct responsibility of Subcommittee F01.17 on Sputter Metallization.Current
15、 edition approved June 1, 2011. Published June 2011. Originallyapproved in 1998. Last previous edition approved in 2003 as F189498 (03). DOI:10.1520/F1894-98R11.2The boldface numbers in parentheses refer to a list of references at the end ofthe text.3For referenced ASTM standards, visit the ASTM web
16、site, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United Sta
17、tes.3.2.1 WSixa tungsten silicide film characterized by asilicon/tungsten atomic ratio 2.00.3.2.2 incident ionsHe+or He+ions with energy in therange of 2.25 to 2.30 MeV delivered to a sample surface froman appropriate ion source and accelerator system.3.2.3 backscattered ionsHelium particles (charge
18、d orneutral) recoiling from atoms in a sample structure irradiatedwith a collimated beam of incident ions.3.2.4 RBSRutherford backscattering spectromerty, the en-ergy analysis of backscattered ions for sample composition anddepth profile.3.2.5 normal angle detectora detector situated at an anglebetw
19、een 160 and 180 from the forward trajectory of theincident ion.3.2.6 grazing angle detectora detector situated at an anglebetween 90 to 130 from the forward trajectory of the incidention beam.4. Summary of Test Method4.1 Fig. 1 shows a schematic of the measurement technique.A collimated beam of alph
20、a particles (He+) is incident on thesample surface. A fraction of the incident ions are scattered outof the specimen with backscattered energies corresponding tothe atomic presence of elements in the sample at correspondingdepths.4.2 Spectra of the energy of backscattered ions are acquiredat normal
21、and grazing angle detectors for a measured quantityof integrated ion charge on the sample. The grazing angledetector is movable in order to maintain appropriate depthresolution for films of various thicknesses. The grazing angledetector position is chosen to provide a wide tungsten signal(increasing
22、 depth resolution) without causing an overlap of thetungsten and silicon signals. The normal angle detector is heldfixed to provide accuracy and reproducibility over manymonths.4.3 The spectra are analyzed for film composition andthickness using standard software packages. Requirements onthe paramet
23、ers used in software are enumerated in Section 13.5. Significance and Use5.1 This test method can be used to ensure absolute repro-ducibility of WSixfilm deposition systems over the course ofmany months. The time span of measurements is essentiallythe life of many process deposition systems.5.2 This
24、 test method can be used to qualify new WSixdeposition systems to ensure duplicability of existing systems.This test method is essential for the coordination of globalsemiconductor fabrication operations using different analyticalservices. This test method allows samples from various depo-sition sys
25、tems to be analyzed at different sites and times.5.3 This test method is the chosen calibration technique fora variety of analytical techniques, including, but not limited to:5.3.1 Electron spectroscopy for chemical analysis (ESCAorXPS),5.3.2 Auger electron spectroscopy (AES),5.3.3 Fourier transform
26、 infrared red spectroscopy (FTIR),5.3.4 Secondary ion mass spectrometry (SIMS), and5.3.5 Electron dispersive spectrometry (EDS) and particleinduced x-ray emission (PIXE).6. Interferences6.1 Since RBS is a measurement of the energy loss sufferedby energetic helium atoms from atomic masses, the interf
27、er-ence of signals results if two or more atoms in the same layerhave roughly the same atomic number (Z). The separation ofatomic numbers necessary for detectable, independent signalsvaries depending on the mass range of the element in question(1). Masses in the range of 12030 monthsF1894 98 (2011)4
28、NOTE 1Since the values were obtained from various samples with widely varying compositions, the ratios are normalized by originally measured silicon/tungsten ratios.FIG. 4 Running Plot of Measured Silicon/Tungsten Ratios Obtained in an SPC Program.F189498(2011)5generated from the theoretical model i
29、s then produced. Thegrazing angle detector spectrum yields the most precise depthresolution of the tungsten and silicon. The normal angledetector spectrum yields the most accurate layer thicknessesand silicon/tungsten ratios.13.3 For standardization of this test method, it is stronglyrecommended tha
30、t the stopping power coefficients as deter-mined by Ziegler and Chu (3) and reproduced in Table VII ofChu, Mayer, and Nicolet (1) be used in the data reduction of thetungsten and silicon signal heights. This suggestion is madedue to the near-universal recognition of and accessibility to thetext as a
31、n RBS reference. The polynomial fit to the (4) heliumstopping cross-section is reproduced here as follows:5A01 A1E 1 A2E21 A3E31 A4E41 A5E5(1)for tungsten, where the coefficients are:A0= 61.69A1= 156.6A2= 150.9A3= 62.45A4= 12.33, andA5= 0.9421.for silicon, where the coefficients are:A0= 57.97A1= 56.
32、59A2= 77.66A3= 36.41A4= 7.624, andA5= 0.5995.13.4 Subtract the minimum background of the 160 spec-trum between the silicon and tungsten signals. Set the effectivesolid angle of the spectra by normalizing the theoretical modelto the experimental spectrum at the tungsten signal. Determinethe silicon/t
33、ungsten ratio from the 160 spectrum. Determinethe depth profile of the tungsten from the grazing anglespectrum.13.5 The theoretical model assumes that layers in the WSixfilms are comprised of tungsten in WSi2(hexagonal) bonds andexcess elemental silicon. This theoretical approach assumesthat all tun
34、gsten is incorporated into WSi2bonds. The densityof the WSixfilm is then an upper limit on the actual filmdensity and generates a lower limit on the thickness. The RBSformulation arises from the relation that the product of the filmthickness and film density is the fundamental unit of measure-ment (
35、atoms/cm2) in RBS. Film thicknesses determined by thisapproach have demonstrated accuracies to within 10 % com-pared to thicknesses determined from SEM cross-sections (6).14. Report14.1 Report the important experimental parameters with thefollowing results:14.1.1 Sample and laboratory identification
36、,14.1.2 Energy of the incident ion beam,14.1.3 Angle settings of the normal and grazing angledetectors, and14.1.4 Date of measurement (for traceability to SPC re-cords).14.2 Report secondary experimental parameters for archivalpurposes although not critical to presentation of results asfollows:14.2.
37、1 Energy per channel calibration,14.2.2 Surface elemental markers (channel numbers) forrelevant elements,14.2.3 Software name and version, and14.2.4 Operator.15. Precision and Bias15.1 PrecisionThe precision of this test method is deter-mined from step heights observed in the tungsten signal fromnum
38、erous films. The accuracy of this test method is reinforcedfrom the measurement of the bismuth implant “standard” (4, 5)and the stringency of the SPC program.15.2 The accuracy of film thicknesses is based on compari-son to SEM cleave and cross-section measurements (6). TheSEM instrument is calibrate
39、d to NIST standards and providesbasis for accuracy (see Annex A1 for details on the thicknessdetermination).16. Keywords16.1 analysis of tungsten silicide; backscattering analysis;composition; metallization films; quantitative analysis; RBS;WSixANNEX(Mandatory Information)A1. EQUATIONS GOVERNING DEN
40、SITY CALCULATION OF WSixFILMSA1.1 The atomic density (in units of atoms/cm3)ofaWSixfilm is calculated by assuming that the film is comprised ofWSi2plus excess elemental silicon. The equation used tocalculate the film density from the atomic concentration ofeach layer is as follows:DWSix5 3 3 fw3 DWS
41、i21 fSi2 2 3 fW! 3 DSi5 fWSi23 DWSi21 fSi3 DSi. (A1.1)A1.2 The density of a layer is related to the thickness of alayer because the product yields the areal concentration (inunits of atoms/cm2) of the elemental signals. The areal con-centration is the fundamental unit measured in an RBSanalysis.A1.3
42、 It is assumed that all tungsten is incorporated intoWSi2unit cell. Thus, thicknesses determined from Eq A1.1 is alower limit on the actual film thickness.F1894 98 (2011)6REFERENCES(1) Chu, W. K., Mayer, Nicolet, Backscattering Spectrometry, AcademicPress, New York, 1978.(2) Handbook of Modern Ion B
43、eam Materials Analysis, Ed. J.R. Tesmerand M. Nastasi, Materials Research Society, Pittsburgh, PA 15237USA, 1995.(3) Ziegler, J.F., and Chu, W.K. Atomic Data Nuclear Data Tables,Vol13, 1974, p. 483.(4) Cohen, C., Davies, J.A., Drigo A.V., and Jackman, T.E. Nucl. Inst.Meth, Vol 218, 1983, p.147.(5) D
44、avies, J.A., Jackman, T.E., Eschbach, H.L., Domba, W., Watjen, U.,and Chivers, D. Nucl. Inst. Meth, Vol B15, p. 238.(6) “Determination of Accurate Metal Silicide Layer Thickness by RBS”,Kirchhoff, J.F., Baumann, S. M., Evans, C., Ward, I., Conveney, P.,Nucl. Instr. Meth Vol B 99 pp. 476-478.ASTM Int
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48、andards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).F1894 98 (2011)7
