ASTM F1894-98
(Test Method)Test Method for Quantifying Tungsten Silicide Semiconductor Process Films for Composition and Thickness
Test Method for Quantifying Tungsten Silicide Semiconductor Process Films for Composition and Thickness
SCOPE
1.1 This test method covers the quantitative determination of tungsten and silicon concentrations in tungsten/silicon (WSIx), semiconductor process films using Rutherford Backscattering Spectrometry (RBS). (1) This test method also covers the detection and quantification of impurities in the mass range from phosphorus A (31 atomic mass units (amu) to antimony (122 amu).
1.2 This test method can be used for tungsten silicide films prepared by any deposition or annealing processes, or both. The film must be a uniform film with an areal coverage greater than the incident ion beam (~2.5 mm).
1.3 This test method accurately measures he following film properties: silicon/tungsten ratio and variations with depth, tungsten depth profile throughout film, WSIx, film thickness, argon concentrations (if present), presence of oxide on surface of WSIx films, and transition metal impurities to detection limits of 1 x 10 14 atoms/cm2.
1.4 This test method can detect absolute differences in silicon and tungsten concentrations of +/- 3 and +/- 1 atomic percent, respectively, measured from different samples in separate analyses. relative variations in the tungsten concentration in depth can be detected to +/- 0.2 atomic percent with a depth resolution of +/- 70A.
1.5 This test method supports and assists in qualifying WSIx films by electrical resistivity techniques.
1.6 This test method can be performed for WSIx films deposited on conducting or insulating substrates.
1.7 This test method is useful for WSIx films between 20 and 400 mm with an areal coverage of greater than 1 by 1 mm.
1.8 This test method is non-destructive to the film to the extent of sputtering.
1.9 A statistical process control (SPC) of WSIx films has been monitored since 1993 with reproducibility to +/- 4%.
1.10 This test method produces accurate film thicknesses by modeling the film density of the WSIx film as WSI2 (hexagonal) plus excess elemental SI2. The measured film thickness is a lower limit to the actual film thickness with an accuracy less than 10% compared to SEM cross-section measurements (see 13.4)
1.11 This test method can be used to analyze films on whole wafers up to 300 mm without breaking the wafers. The sites that can be analyzed may be restricted to concentric rings near the wafer edges for 200-mm and 300-mm wafers, depending on system capabilities.
1.12 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F 1894 – 98
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Test Method for
Quantifying Tungsten Silicide Semiconductor Process Films
1
for Composition and Thickness
This standard is issued under the fixed designation F 1894; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope than 10 % compared to SEM cross-section measurements (see
13.4).
1.1 This test method covers the quantitative determination
1.11 This test method can be used to analyze films on whole
of tungsten and silicon concentrations in tungsten/silicon
wafers up to 300 mm without breaking the wafers. The sites
(WSi ) semiconductor process films using Rutherford Back-
x
2
that can be analyzed may be restricted to concentric rings near
scattering Spectrometry (RBS). (1) This test method also
the wafer edges for 200-mm and 300-mm wafers, depending
covers the detection and quantification of impurities in the
on system capabilities.
mass range from phosphorus Å (31 atomic mass units (amu) to
1.12 This standard does not purport to address all of the
antimony (122 amu).
safety concerns, if any, associated with its use. It is the
1.2 This test method can be used for tungsten silicide films
responsibility of the user of this standard to establish appro-
prepared by any deposition or annealing processes, or both.
priate safety and health practices and determine the applica-
The film must be a uniform film with an areal coverage greater
bility of regulatory limitations prior to use. The reader is
than the incident ion beam (;2.5 mm).
referenced to Section 8 of this test method for references to
1.3 This test method accurately measures the following film
some of the regulatory, radiation, and safety considerations
properties: silicon/tungsten ratio and variations with depth,
involved with accelerator operation.
tungsten depth profile throughout film, WSi film thickness,
x
argon concentrations (if present), presence of oxide on surface
2. Referenced Documents
of WSi films, and transition metal impurities to detection
x
14 2
2.1 Terminology used in this document is consistent with
limits of 1310 atoms/cm .
terms and definitions as used in the Compilation of ASTM
1.4 This test method can detect absolute differences in
th
Standard Definitions,8 ed ASTM, 1994, Philadelphia PA,
silicon and tungsten concentrations of 63 and 61 atomic
USA, specifically for terms taken from the following ASTM
percent, respectively, measured from different samples in
standards:
separate analyses. Relative variations in the tungsten concen-
2.2 ASTM Standards:
tration in depth can be detected to 60.2 atomic percent with a
E 135 Terminology of Analytical Chemistry for Metals,
depth resolution of 670Å.
3
Ores, and Related Materials
1.5 This test method supports and assists in qualifying WSi
x
4
E 673 Terminology Relating to Surface Analysis
films by electrical resistivity techniques.
5
E 1241 Terminology of Semiconductor Technology
1.6 This test method can be performed for WSi films
x
deposited on conducting or insulating substrates.
3. Terminology
1.7 This test method is useful for WSi films between 20 and
x
2 3.1 Numerous terms specific to RBS and ion stopping in
400 nm with an areal coverage of greater than 1 by 1 mm .
2
solids can be found in the following references (1, 2) .
1.8 This test method is non-destructive to the film to the
3.2 Definitions of Terms Specific to This Standard:
extent of sputtering.
3.2.1 WSi —a tungsten silicide film characterized by a
x
1.9 A statistical process control (SPC) of WSi films has
x
silicon/tungsten atomic ratio >2.00.
been monitored since 1993 with reproducibility to 64%.
+ ++
3.2.2 incident ions—He or He ions with energy in the
1.10 This test method produces accurate film thicknesses by
range of 2.25 to 2.30 MeV delivered to a sample surface from
modeling the film density of the WSi film as WSi (hexagonal)
x 2
2 an appropriate ion source and accelerator system.
plus excess elemental Si . The measured film thickness is a
3.2.3 backscattered ions—Helium particles (charged or neu-
lower limit to the actual film thickness with an accuracy less
tral) recoiling from atoms in a sample structure irradiated with
a collimated beam of incident ions.
1
This test method is under the jurisdiction of Committee F-1 on Electronics, and
is the direct responsibility of Subcommittee F01.06 on Silicon Materials and Process
Control.
3
Current edition approved May 10, 1998. Published July 1998. Annual Book of ASTM Standards, Vol 03.05.
2 4
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