ASTM F1894-98(2003)

Test Method for Quantifying Tungsten Silicide Semiconductor Process Films for Composition and Thickness

SIGNIFICANCE AND USE
This test method can be used to ensure absolute reproducibility of WSix film deposition systems over the course of many months. The time span of measurements is essentially the life of many process deposition systems.
This test method can be used to qualify new WSix  deposition systems to ensure duplicability of existing systems. This test method is essential for the coordination of global semiconductor fabrication operations using different analytical services. This test method allows samples from various deposition systems to be analyzed at different sites and times.
This test method is the chosen calibration technique for a variety of analytical techniques, including, but not limited to:
5.3.1 Electron spectroscopy for chemical analysis (ESCA or XPS),
5.3.2 Auger electron spectroscopy (AES),
5.3.3 Fourier transform infrared red spectroscopy (FTIR),
5.3.4 Secondary ion mass spectrometry (SIMS), and
5.3.5 Electron dispersive spectrometry (EDS) and particle induced x-ray emission (PIXE).
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. The reader is referenced to Section 8 of this test method for references to some of the regulatory, radiation, and safety considerations involved with accelerator operation.

General Information

• Status: Historical
• Publication Date: 09-May-1998
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics
• Drafting Committee: F01.17 - Sputter Metallization

Relations

• Replaces: ASTM F1894-98 - Test Method for Quantifying Tungsten Silicide Semiconductor Process Films for Composition and Thickness
• Effective Date: 10-May-1998
• Replaced By: ASTM F1894-98(2011) - Test Method for Quantifying Tungsten Silicide Semiconductor Process Films for Composition and Thickness (Withdrawn 2020)
• Effective Date: 01-Jun-2011

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:F1894–98 (Reapproved2003)
Test Method for
Quantifying Tungsten Silicide Semiconductor Process Films
for Composition and Thickness
This standard is issued under the fixed designation F1894; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope plus excess elemental Si . The measured film thickness is a
lower limit to the actual film thickness with an accuracy less
1.1 This test method covers the quantitative determination
than 10 % compared to SEM cross-section measurements (see
of tungsten and silicon concentrations in tungsten/silicon
13.4).
(WSi ) semiconductor process films using Rutherford Back-
x
1.11 Thistestmethodcanbeusedtoanalyzefilmsonwhole
scattering Spectrometry (RBS). (1) This test method also
wafers up to 300 mm without breaking the wafers. The sites
covers the detection and quantification of impurities in the
that can be analyzed may be restricted to concentric rings near
mass range from phosphorus Å (31 atomic mass units (amu) to
the wafer edges for 200-mm and 300-mm wafers, depending
antimony (122 amu).
on system capabilities.
1.2 This test method can be used for tungsten silicide films
1.12 This standard does not purport to address all of the
prepared by any deposition or annealing processes, or both.
safety concerns, if any, associated with its use. It is the
The film must be a uniform film with an areal coverage greater
responsibility of the user of this standard to establish appro-
than the incident ion beam (;2.5 mm).
priate safety and health practices and determine the applica-
1.3 This test method accurately measures the following film
bility of regulatory limitations prior to use. The reader is
properties: silicon/tungsten ratio and variations with depth,
referenced to Section 8 of this test method for references to
tungsten depth profile throughout film, WSi film thickness,
x
some of the regulatory, radiation, and safety considerations
argon concentrations (if present), presence of oxide on surface
involved with accelerator operation.
of WSi films, and transition metal impurities to detection
x
14 2
limits of 1310 atoms/cm .
2. Referenced Documents
1.4 This test method can detect absolute differences in
2.1 Terminology used in this document is consistent with
silicon and tungsten concentrations of 63 and 61 atomic
terms and definitions as used in the Compilation of ASTM
percent, respectively, measured from different samples in
th
Standard Definitions,8 ed ASTM, 1994, Philadelphia PA,
separate analyses. Relative variations in the tungsten concen-
USA, specifically for terms taken from the following ASTM
tration in depth can be detected to 60.2 atomic percent with a
standards:
depth resolution of 670Å.
2.2 ASTM Standards:
1.5 ThistestmethodsupportsandassistsinqualifyingWSi
x
E135 Terminology Relating to Analytical Chemistry for
films by electrical resistivity techniques.
Metals, Ores, and Related Materials
1.6 This test method can be performed for WSi films
x
E673 Terminology Relating to Surface Analysis
deposited on conducting or insulating substrates.
E1241 Guide for Conducting Early Life-Stage Toxicity
1.7 ThistestmethodisusefulforWSi filmsbetween20and
x
2 Tests with Fishes
400 nm with an areal coverage of greater than 1 by 1 mm .
1.8 This test method is non-destructive to the film to the
3. Terminology
extent of sputtering.
3.1 Numerous terms specific to RBS and ion stopping in
1.9 A statistical process control (SPC) of WSi films has
x
solids can be found in the following references (1, 2) .
been monitored since 1993 with reproducibility to 64%.
3.2 Definitions of Terms Specific to This Standard:
1.10 This test method produces accurate film thicknesses by
3.2.1 WSi —a tungsten silicide film characterized by a
x
modelingthefilmdensityoftheWSi filmasWSi (hexagonal)
x 2
silicon/tungsten atomic ratio >2.00.
This test method is under the jurisdiction of Committee F01 on Electronics ,
and is the direct responsibility of Subcommittee F01.17 on Sputter Metallization.
Current edition approved Dec. 1, 2003. Published July 1998. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
F1894-98R03. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
the text. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F1894–98 (2003)
+ ++
3.2.2 incident ions—He or He ions with energy in the 4.3 The spectra are analyzed for film composition and
range of 2.25 to 2.30 MeV delivered to a sample surface from thickness using standard software packages. Requirements on
an appropriate ion source and accelerator system. the parameters used in software are enumerated in Section 13.
3.2.3 backscattered ions—Helium particles (charged or
5. Significance and Use
neutral) recoiling from atoms in a sample structure irradiated
5.1 This test method can be used to ensure absolute repro-
with a collimated beam of incident ions.
ducibility of WSi film deposition systems over the course of
3.2.4 RBS—Rutherfordbackscatteringspectromerty,theen-
x
many months. The time span of measurements is essentially
ergyanalysisofbackscatteredionsforsamplecompositionand
the life of many process deposition systems.
depth profile.
5.2 This test method can be used to qualify new WSi
3.2.5 normal angle detector—a detector situated at an angle x
deposition systems to ensure duplicability of existing systems.
between 160 and 180° from the forward trajectory of the
This test method is essential for the coordination of global
incident ion.
semiconductor fabrication operations using different analytical
3.2.6 grazing angle detector—adetectorsituatedatanangle
services. This test method allows samples from various depo-
between 90 to 130° from the forward trajectory of the incident
sition systems to be analyzed at different sites and times.
ion beam.
5.3 This test method is the chosen calibration technique for
a variety of analytical techniques, including, but not limited to:
4. Summary of Test Method
5.3.1 Electron spectroscopy for chemical analysis (ESCAor
4.1 Fig.1showsaschematicofthemeasurementtechnique.
XPS),
++
Acollimated beam of alpha particles (He ) is incident on the
5.3.2 Auger electron spectroscopy (AES),
sample surface.Afraction of the incident ions are scattered out
5.3.3 Fourier transform infrared red spectroscopy (FTIR),
of the specimen with backscattered energies corresponding to
5.3.4 Secondary ion mass spectrometry (SIMS), and
theatomicpresenceofelementsinthesampleatcorresponding
5.3.5 Electron dispersive spectrometry (EDS) and particle
depths.
induced x-ray emission (PIXE).
4.2 Spectra of the energy of backscattered ions are acquired
at normal and grazing angle detectors for a measured quantity
6. Interferences
of integrated ion charge on the sample. The grazing angle
6.1 Since RBS is a measurement of the energy loss suffered
detector is movable in order to maintain appropriate depth
by energetic helium atoms from atomic masses, the interfer-
resolution for films of various thicknesses. The grazing angle
ence of signals results if two or more atoms in the same layer
detector position is chosen to provide a wide tungsten signal
have roughly the same atomic number (Z). The separation of
(increasing depth resolution) without causing an overlap of the
atomic numbers necessary for detectable, independent signals
tungsten and silicon signals. The normal angle detector is held
varies depending on the mass range of the element in question
fixed to provide accuracy and reproducibility over many
(1).Massesintherangeof120 months.
from tungsten in a 1500Å WSi film.
x
6.2 The detection limits of atmospheric elements (fluorine,
nitrogen, oxygen, and carbon) inWSi films are 5 to 15 atomic
x
% due to interference between the signals from these elements
andsignalsfromsubstratesilicon,siliconoxide,siliconnitride,
or polysilicon layers that may be present in the sample
structure.
6.3 The accuracy of this test method may be degraded by
nonuniformity or interface roughness of theWSi film. Rough-
x
nessofthesurfaceorinterfacesofthesampledegradesthelow
energy edge of the tungsten and silicon and reduces the
accuracy of the theoretical modeling used to describe the
interfaces.
6.4 Energy of the incident ion beam and detector resolution
directly impact the quality of the acquired experimental spec-
tra. A lack of resolution due to the poor control of either of
these parameters degrades the accuracy of the depth profiling
of the tungsten in the WSi film.
x
6.5 It is necessary to restrict the beam current on samples to
<80 nA. Currents in excess of this for most detection apparati
may result in signal pile-up in the detector electronics and
degrade the accuracy of the measurement.
7. Apparatus
NOTE 1—The grazing angle detector is movable to improve depth
7.1 RBS Instrument, consists of a source for a monoener-
resolution of the WSi films.
x
+
FIG. 1 Schematic Diagram of RBS Experimental Arrangement getic, well-collimated beam of helium ions (He or alpha
F1894–98 (2003)
particles). This source typically is comprised of an ion source, from a sputter deposited WSi film on a polycrystalline
x
accelerator, and energy-momentum selector magnetic sector. Si/SiO /singlecrystalsiliconstructureata160°(normalangle)
TheanalysisofgeneralRBSdataisoptimallyperformedforan detector and a 110° (grazing angle) detector.
incident ion beam energy of 2.0 to 2.4 MeV. The data 7.4 Spectra at the normal angle and grazing angle detectors
-5
acquisition is performed in an evacuated (pressure <1310 are acquired for a measured quantity of charge. The grazing
Torr) end chamber that is equipped with necessary data angle detector is movable in order to maintain appropriate
acquisition electronics. Data acquisition and analysis should depth resolution for films of various thicknesses. The grazing
proceed with the use of applicable software. angle detector position is chosen to provide a wide tungsten
++
7.2 The energy of the collimated alpha particle (He ) ion signal (increasing depth resolution) without causing an overlap
beamisrestrictedtotherangeof2.25to2.30MeV.Thehelium of the tungsten and silcon signals.The normal angle detector is
ions have a range of ;3-5 µm in the sample although only held fixed to provide accuracy and reproducibility over many
collisions occurring in the top ;1.5 µm result in a backscat- months.
tered event detectable at the normal angle detector. This depth 7.5 The grazing angle detector spectrum must be acquired
is limited to <1 µm for helium atoms backscattered toward the with the sample surface fixed with respect to the incident ion
grazing angle detector.The detectors are silicon surface barrier beam. The fixed orientation is performed with the sample
detectors. normal aligned parallel with respect to the incident ion beam.
7.3 The majority of the incident alpha particles are im- The spectra from the grazing angle detector are used to
planted in the specimen. A fraction of the incident ions are measure an accurate depth profile of the tungsten in the film.
scattered out of the specimen with backscattered energies Since the grazing angle detector is sensitive to surface layers,
corresponding to the presence of elements in the sample at accurate information for layers deeper than ;3000Å is not
corresponding depths. Fig. 2 shows sample spectra acquired obtainable from the grazing angle detector spectrum.
NOTE 1—The detector angle setting can be found in the upper, right legend of the figures.The contributions from each element and layer is highlighted
on the figures. This sample exhibits significant tungsten enrichment at the WSi /poly silicon interface, The theoretical model (upper, left legend of top
x
spectrum) is read as layer thickness (Å), element, and atomic concentration. The model shown is for the WSi film only. The substrate structure is
x
Si/SiO /poly silicon.
FIG. 2 Spectra From the Normal and Grazing Angle Detectors
F1894–98 (2003)
7.6 Thenormalangledetectorspectrumisacquiredwiththe 11.2 Reproducibility of the RBS measurement is ensured
sample orientation manipulated in a way that prevents ion through a statistical process control (SPC) program. The SPC
channeling in any single crystal layers or substrates. This is program measures a WSi sample 2 to 3 times weekly for
x
referred to as a “random” orientation. The signal from the various film properties. These properties must lie within tight
randomorientationisthusnormalizablefromsampletosample reproducibility limits for the instrument to be in control (see
and allows quantitative comparison of the WSi films on Fig.3,Fig.4).Thespectraarealsoinspectedforanomaliesthat
x
multiple samples. cannot be measured quantitatively.
7.7 Since there is essentially no sample degradation due to
12. Measurement Procedures
dataacquisition,suitablereferencesamplecanbecleavedfrom
any previously analyzed sample. This reference sample can 12.1 Ensure that the instrument is in control as indicated by
then be used as a statistical process control (SPC) sample for themostrecentacquisitionandanalysisofaspectrumfromthe
periods ranging from several to many months, depending on SPC sample. Any significant change in system electronics or
the size and uniformity of the film on the reference sample. beam energy warrants the acquisition and analysis of new SPC
This sample should be used for reproducibility evaluation only data.
and should not substitute for periodic system calibrations. 12.2 Mount the sample(s) on a conducting sample holder
7.8 Sample preparation may be performed in ambient con-
and place in acquisition chamber. Evacuate acquisition cham-
-5
ditions.Careshouldbetakentoavoidintroducingimpuritiesto ber to at least 1 3 10 Torr or better.Absolute vacuum should
-6
the surface of samples other than unavoidable adsorbed atmo-
be <53 10 Torr or better.
spherics. 12.3 Choose the appropriate grazing angle detector setting
(see 7.3, 7.4, and 7.5). Record the settings of the normal and
8. Hazards
grazing angle detectors, the total charge intergration, the
energy of the incident ion beam, and the sample orientation for
8.1 This test method employs a particle accelerator. All
each experimental spectrum.
necessary and recommended safety precautions fo
...