ASTM F1894-98(2011)

Test Method for Quantifying Tungsten Silicide Semiconductor Process Films for Composition and Thickness (Withdrawn 2020)

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:
Electron spectroscopy for chemical analysis (ESCA or XPS),
Auger electron spectroscopy (AES),
Fourier transform infrared red spectroscopy (FTIR),
Secondary ion mass spectrometry (SIMS), and
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 Å (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 the 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 1×1014 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 ±70Å.
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 nm with an areal coverage of greater than 1 by 1 mm2.
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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.13 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.
WITHD...

General Information

• Status: Withdrawn
• Publication Date: 31-May-2011
• Withdrawal Date: 09-Jan-2020
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics
• Drafting Committee: F01.17 - Sputter Metallization

Relations

• Replaces: ASTM F1894-98(2003) - Test Method for Quantifying Tungsten Silicide Semiconductor Process Films for Composition and Thickness
• 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 (Reapproved 2011)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.9 A statistical process control (SPC) of WSi films has
x
been monitored since 1993 with reproducibility to 64%.
1.1 This test method covers the quantitative determination
of tungsten and silicon concentrations in tungsten/silicon
1.10 Thistestmethodproducesaccuratefilmthicknessesby
(WSi ) semiconductor process films using Rutherford Back-
x modelingthefilmdensityoftheWSi filmasWSi (hexagonal)
x 2
scattering Spectrometry (RBS). (1) This test method also
plus excess elemental Si . The measured film thickness is a
covers the detection and quantification of impurities in the
lower limit to the actual film thickness with an accuracy less
massrangefromphosphorusÅ(31atomicmassunits(amu)to
than 10% compared to SEM cross-section measurements (see
antimony (122 amu).
13.4).
1.2 This test method can be used for tungsten silicide films
1.11 Thistestmethodcanbeusedtoanalyzefilmsonwhole
prepared by any deposition or annealing processes, or both.
wafers up to 300 mm without breaking the wafers. The sites
Thefilmmustbeauniformfilmwithanarealcoveragegreater
that can be analyzed may be restricted to concentric rings near
than the incident ion beam (;2.5 mm).
the wafer edges for 200-mm and 300-mm wafers, depending
1.3 Thistestmethodaccuratelymeasuresthefollowingfilm
on system capabilities.
properties: silicon/tungsten ratio and variations with depth,
1.12 The values stated in SI units are to be regarded as
tungsten depth profile throughout film, WSi film thickness,
x
standard. No other units of measurement are included in this
argon concentrations (if present), presence of oxide on surface
standard.
of WSi films, and transition metal impurities to detection
x
14 2
limits of 1×10 atoms/cm .
1.13 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.4 This test method can detect absolute differences in
responsibility of the user of this standard to establish appro-
silicon and tungsten concentrations of 63 and 61 atomic
priate safety and health practices and determine the applica-
percent, respectively, measured from different samples in
bility of regulatory limitations prior to use. The reader is
separate analyses. Relative variations in the tungsten concen-
referenced to Section 8 of this test method for references to
tration in depth can be detected to 60.2 atomic percent with a
some of the regulatory, radiation, and safety considerations
depth resolution of 670Å.
involved with accelerator operation.
1.5 ThistestmethodsupportsandassistsinqualifyingWSi
x
films by electrical resistivity techniques.
2. Referenced Documents
1.6 This test method can be performed for WSi films
x
2.1 Terminology used in this document is consistent with
deposited on conducting or insulating substrates.
terms and definitions as used in the Compilation of ASTM
th
1.7 ThistestmethodisusefulforWSi filmsbetween20and
x Standard Definitions,8 ed ASTM, 1994, Philadelphia PA,
400 nm with an areal coverage of greater than 1 by 1 mm .
USA, specifically for terms taken from the following ASTM
standards:
1.8 This test method is non-destructive to the film to the
extent of sputtering. 3
2.2 ASTM Standards:
E135Terminology Relating to Analytical Chemistry for
Metals, Ores, and Related Materials
ThistestmethodisunderthejurisdictionofCommitteeF01onElectronics,and
is the direct responsibility of Subcommittee F01.17 on Sputter Metallization.
Current edition approved June 1, 2011. Published June 2011. Originally
approved in 1998. Last previous edition approved in 2003 as F1894–98 (03). DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/F1894-98R11. 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 (2011)
++
E673TerminologyRelatingtoSurfaceAnalysis(Withdrawn Acollimated beam of alpha particles (He ) is incident on the
2012) samplesurface.Afractionoftheincidentionsarescatteredout
E1241GuideforConductingEarlyLife-StageToxicityTests of the specimen with backscattered energies corresponding to
with Fishes theatomicpresenceofelementsinthesampleatcorresponding
depths.
3. Terminology
4.2 Spectra of the energy of backscattered ions are acquired
3.1 Numerous terms specific to RBS and ion stopping in
at normal and grazing angle detectors for a measured quantity
solids can be found in the following references (1, 2) .
of integrated ion charge on the sample. The grazing angle
3.2 Definitions of Terms Specific to This Standard: detector is movable in order to maintain appropriate depth
3.2.1 WSi —a tungsten silicide film characterized by a resolution for films of various thicknesses. The grazing angle
x
silicon/tungsten atomic ratio >2.00. detector position is chosen to provide a wide tungsten signal
+ ++
(increasingdepthresolution)withoutcausinganoverlapofthe
3.2.2 incident ions—He or He ions with energy in the
tungsten and silicon signals.The normal angle detector is held
range of 2.25 to 2.30 MeV delivered to a sample surface from
fixed to provide accuracy and reproducibility over many
an appropriate ion source and accelerator system.
months.
3.2.3 backscattered ions—Heliumparticles(chargedorneu-
tral) recoiling from atoms in a sample structure irradiated with 4.3 The spectra are analyzed for film composition and
thickness using standard software packages. Requirements on
a collimated beam of incident ions.
the parameters used in software are enumerated in Section 13.
3.2.4 RBS—Rutherford backscattering spectromerty, the en-
ergyanalysisofbackscatteredionsforsamplecompositionand
5. Significance and Use
depth profile.
5.1 This test method can be used to ensure absolute repro-
3.2.5 normal angle detector—a detector situated at an angle
ducibility of WSi film deposition systems over the course of
between 160 and 180° from the forward trajectory of the
x
many months. The time span of measurements is essentially
incident ion.
the life of many process deposition systems.
3.2.6 grazing angle detector—adetectorsituatedatanangle
between 90 to 130° from the forward trajectory of the incident
5.2 This test method can be used to qualify new WSi
x
ion beam.
deposition systems to ensure duplicability of existing systems.
This test method is essential for the coordination of global
4. Summary of Test Method
semiconductor fabrication operations using different analytical
4.1 Fig.1showsaschematicofthemeasurementtechnique. services. This test method allows samples from various depo-
sition systems to be analyzed at different sites and times.
5.3 This test method is the chosen calibration technique for
The last approved version of this historical standard is referenced on
avarietyofanalyticaltechniques,including,butnotlimitedto:
www.astm.org.
5.3.1 Electronspectroscopyforchemicalanalysis(ESCAor
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).
6. Interferences
6.1 Since RBS is a measurement of the energy loss suffered
by energetic helium atoms from atomic masses, the interfer-
ence of signals results if two or more atoms in the same layer
have roughly the same atomic number (Z). The separation of
atomic numbers necessary for detectable, independent signals
varies depending on the mass range of the element in question
(1).Massesintherangeof120 from tungsten in a 1500Å WSi film.
x
6.2 The detection limits of atmospheric elements (fluorine,
nitrogen,oxygen,andcarbon)inWSi filmsare5to15atomic
x
% due to interference between the signals from these elements
andsignalsfromsubstratesilicon,siliconoxide,siliconnitride,
NOTE 1—The grazing angle detector is movable to improve depth
or polysilicon layers that may be present in the sample
resolution of the WSi films.
x
FIG. 1 Schematic Diagram of RBS Experimental Arrangement structure.
F1894 − 98 (2011)
6.3 The accuracy of this test method may be degraded by source, accelerator, and energy-momentum selector magnetic
nonuniformityorinterfaceroughnessoftheWSi film.Rough- sector. The analysis of general RBS data is optimally per-
x
nessofthesurfaceorinterfacesofthesampledegradesthelow formedforanincidentionbeamenergyof2.0to2.4MeV.The
energy edge of the tungsten and silicon and reduces the data acquisition is performed in an evacuated (pressure
-5
accuracy of the theoretical modeling used to describe the <1×10 Torr)endchamberthatisequippedwithnecessarydata
interfaces. acquisition electronics. Data acquisition and analysis should
proceed with the use of applicable software.
6.4 Energy of the incident ion beam and detector resolution
++
directly impact the quality of the acquired experimental spec- 7.2 The energy of the collimated alpha particle (He ) ion
tra. A lack of resolution due to the poor control of either of
beamisrestrictedtotherangeof2.25to2.30MeV.Thehelium
these parameters degrades the accuracy of the depth profiling ions have a range of ;3-5 µm in the sample although only
of the tungsten in the WSi film.
collisions occurring in the top ;1.5 µm result in a backscat-
x
tered event detectable at the normal angle detector. This depth
6.5 Itisnecessarytorestrictthebeamcurrentonsamplesto
is limited to <1 µm for helium atoms backscattered toward the
<80 nA. Currents in excess of this for most detection apparati
grazingangledetector.Thedetectorsaresiliconsurfacebarrier
may result in signal pile-up in the detector electronics and
detectors.
degrade the accuracy of the measurement.
7.3 The majority of the incident alpha particles are im-
7. Apparatus
planted in the specimen. A fraction of the incident ions are
7.1 RBS Instrument, consists of a source for a scattered out of the specimen with backscattered energies
+
monoenergetic, well-collimated beam of helium ions (He or corresponding to the presence of elements in the sample at
alpha particles). This source typically is comprised of an ion corresponding depths. Fig. 2 shows sample spectra acquired
NOTE1—Thedetectoranglesettingcanbefoundintheupper,rightlegendofthefigures.Thecontributionsfromeachelementandlayerishighlighted
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 (2011)
from a sputter deposited WSi film on a polycrystalline depending on detector active surface area, sample film
x
Si/SiO /singlecrystalsiliconstructureata160°(normalangle) thickness, and sample film roughness. For the measurement of
detector and a 110° (grazing angle) detector. a 1500 Å WSi film using detectors of 50 mm active area, a
x
charge integration of 40 µC per spectrum has been found to be
7.4 Spectra at the normal angle and grazing angle detectors
sufficient for accuracies stated in 1.3, 1.4, and 1.8.
are acquired for a measured quantity of charge. The grazing
angle detector is movable in order to maintain appropriate 9.2 There is no “cross-talk” of data for samples mounted
depth resolution for films of various thicknesses. The grazing close to each other in the data acquisition system.As such, the
angle detector position is chosen to provide a wide tungsten number of mounted samples from which data can be acquired
signal(increasingdepthresolution)withoutcausinganoverlap islimitedonlybythecapabilitiesofthesampleholder,incident
ofthetungstenandsilconsignals.Thenormalangledetectoris ion beam spot size, and the data acquisition software.
held fixed to provide accuracy and reproducibility over many
10. Specimen Requirements
months.
7.5 The grazing angle detector spectrum must be acquired 10.1 Test Specimens must be uniform films with an area
with the sample surface fixed with respect to the incident ion larger than the incident ion beam. The sample surface and
beam. The fixed orientation is performed with the sample interfacesbetweenadjacentlayersshouldberelativelysmooth.
normal aligned parallel with respect to the incident ion beam.
11. Calibration Standards
The spectra from the grazing angle detector are used to
measure an accurate depth profile of the tungsten in the film.
11.1 Results from RBS are quantitative without standards.
Since the grazing angle detector is sensitive to surface layers,
As such, there are no NIST standards for RBS measurements.
accurate information for layers deeper than ;3000Å is not
The RBS instrument is periodically calibrated against a bis-
obtainable from the grazing angle detector spectrum.
muth implant reference sample (3, 4). This sample has been
measured by various RBS instruments and found to contain a
7.6 Thenormalangledetectorspectrumisacquiredwiththe
15 2
bismuth implant of 4.8(64%)×10 Bi atoms/cm .
sample orientation manipulated in a way that prevents ion
channeling in any single crystal layers or substrates. This is
11.2 Reproducibility of the RBS measurement is ensured
referred to as a “random” orientation. The signal from the
through a statistical process control (SPC) program. The SPC
randomorientationisthusnormalizablefromsampletosample
program measures a WSi sample 2 to 3 times weekly for
x
and allows quantitative comparison of the WSi films on
x
various film properties. These properties must lie within tight
multiple samples.
reproducibility limits for the instrument to be in control (see
Fig.3,Fig.4).Thespectraarealsoinspectedforanomaliesthat
7.7 Since there is essentially no sample degradation due to
cannot be measured quantitatively.
dataacquisition,suitablereferencesamplecanbecleavedfrom
any previously analyzed sample. This reference sample can
12. Measurement Procedures
then be used as a statist
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