ASTM F1617-98(2002)
(Test Method)Standard Test Method for Measuring Surface Sodium, Aluminum, Potassium, and Iron on Silicon and EPI Substrates by Secondary Ion Mass Spectrometry (Withdrawn 2003)
Standard Test Method for Measuring Surface Sodium, Aluminum, Potassium, and Iron on Silicon and EPI Substrates by Secondary Ion Mass Spectrometry (Withdrawn 2003)
SCOPE
This standard was transferred to SEMI (www.semi.org) May 2003
1.1 This test method covers the determination of total sodium, aluminum, potassium, and iron on the surface of mirror-polished single crystal silicon and silicon epi substrates using secondary ion mass spectrometry (SIMS). This test method measures the total amount of each metal, because this test method is independent of the metal's chemistry or electrical activity.
1.2 This test method can be used for silicon with all dopant species and dopant concentrations.
1.3 This test method is especially designed to be used for surface metal contamination that is located within approximately 5 nm of the surface of the wafer.
1.4 This test method is especially useful for determining the surface metal areal densities in the native oxide or chemically grown oxide of polished silicon substrates after cleaning.
1.5 This test method is useful for sodium, aluminum, potassium, and iron areal densities between 109 and 1014 atoms/cm 2. The limit of detection is determined by either the BLANK value or by count rate limitations, and may vary with instrumentation.
1.6 This test method is complementary to:
1.6.1 Total reflection X-ray fluorescence (TXRF), that can detect higher atomic number Z, surface metals such as iron, but does not have useful (1011 atoms/cm2) detection limits for sodium, potassium, and aluminum on silicon.
1.6.2 Electron spectroscopy for chemical analysis and Auger electron spectroscopy that can detect metal surface areal densities down to the order of 1012 to 1013 atoms/cm2 .
1.6.3 Vapor phase decomposition (VPD) of surface metals followed by atomic absorption spectroscopy (AAS) or inductively coupled plasma mass spectrometry (ICP-MS) of the VPD residue, where the metal detection limits are 108 to 1010 atoms/cm2. There is no spatial information available and the VPD preconcentration of metals is dependent upon the chemistry of each metal.
1.7 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.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 1617 – 98 (Reapproved 2002)
Standard Test Method for
Measuring Surface Sodium, Aluminum, Potassium, and Iron
on Silicon and EPI Substrates by Secondary Ion Mass
Spectrometry
This standard is issued under the fixed designation F 1617; 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 1.7 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the determination of total
responsibility of the user of this standard to establish appro-
sodium, aluminum, potassium, and iron on the surface of
priate safety and health practices and determine the applica-
mirror-polished single crystal silicon and silicon epi substrates
bility of regulatory limitations prior to use.
using secondary ion mass spectrometry (SIMS). This test
method measures the total amount of each metal, because this
2. Referenced Documents
test method is independent of the metal’s chemistry or electri-
2.1 ASTM Standards:
cal activity.
E 122 Practice for Choice of Sample Size to Estimate a
1.2 This test method can be used for silicon with all dopant
Measure of Quality for a Lot or Process
species and dopant concentrations.
E 673 Terminology Relating to Surface Analysis
1.3 This test method is especially designed to be used for
surface metal contamination that is located within approxi-
3. Terminology
mately 5 nm of the surface of the wafer.
3.1 All terms in this test method are in conformance with
1.4 This test method is especially useful for determining the
those given in Terminology E 673.
surface metal areal densities in the native oxide or chemically
grown oxide of polished silicon substrates after cleaning.
4. Summary of Test Method
1.5 This test method is useful for sodium, aluminum,
9 4.1 Specimens of mirror-polished single crystal silicon are
potassium, and iron areal densities between 10 and
14 2 loaded into a sample holder. The holder is transferred into the
10 atoms/cm . The limit of detection is determined by either
analysis chamber of the SIMS instrument.
the BLANK value or by count rate limitations, and may vary
+
4.2 A primary ion beam, typically O , is used to bombard
with instrumentation.
each specimen with a sputter rate less than 0.015 nm/s (0.9
1.6 This test method is complementary to:
nm/min).
1.6.1 Total reflection X-ray fluorescence (TXRF), that can
4.3 The area of analysis may be different for different
detect higher atomic number Z, surface metals such as iron, but
11 2 instruments and may range from 100 μm 3 100 μm to 1
does not have useful (<10 atoms/cm ) detection limits for
mm 3 1 mm.
sodium, potassium, and aluminum on silicon.
4.4 Depending upon instrumentation, a molecular oxygen
1.6.2 Electron spectroscopy for chemical analysis and Au-
jet or leak may be focused on the analysis area.
ger electron spectroscopy that can detect metal surface areal
23 27 39 54
4.5 The positive secondary ions Na, Al, K, and Fe
12 13 2
densities down to the order of 10 to 10 atoms/cm .
are mass analyzed by a mass spectrometer, and detected by an
1.6.3 Vapor phase decomposition (VPD) of surface metals
electron multiplier (EM) or equivalent high-sensitivity ion
followed by atomic absorption spectroscopy (AAS) or induc-
detector as a function of time until the signals reach back-
tively coupled plasma mass spectrometry (ICP-MS) of the
ground levels or 1 % of the initial signal rates of each element.
8 10
VPD residue, where the metal detection limits are 10 to 10
2 The instrumentation must be able to discriminate the elemental
atoms/cm . There is no spatial information available and the
ion signals from molecular interferences.
VPD preconcentration of metals is dependent upon the chem-
4.6 A BLANK silicon sample is used to evaluate whether
istry of each metal.
the lower limit of detection arises from molecular ion interfer-
ences, elemental instrumental backgrounds, or count rate
This test method is under the jurisdiction of ASTM Committee F01 on
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon
Materials and Process Control.
Current edition approved May 10, 1998. Published July 1998. Originally Annual Book of ASTM Standards, Vol 14.02.
published as F 1617 - 95. Last previous edition F 1617 - 95. Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 1617 – 98 (2002)
limitations. The matrix positive secondary ion count rate for to the measurement. (Particulate room contamination contain-
28 29 30
silicon ( Si, Si, or Si) is measured by a faraday cup (FC) ing these metals is easily distinguished from metal contamina-
or appropriate detector during, or at the end of, the profile. If tion by the shape of the SIMS profile that should have the log
multiple detectors are used during the test, the relative sensi- of the signal drop linearly with time. A particulate contamina-
tivities of the detectors are determined by measuring standard tion does not follow this shape under SIMS profile.)
ion signals (either the same positive secondary ion count rate or 6.2 Bias in the RSFs derived from reference materials can
ion count rates of known relative intensity such as natural Si/ introduce bias into the SIMS measured areal densities.
Si) on each detector. 6.3 Mass interferences can introduce bias if the instrument
23 27 39 54
4.7 The net integrated Na, Al, K, and Fe signals are mass resolution, or subsequent detection scheme, is not suffi-
converted to quantitative areal densities using the detector cient to exclude the interference.
efficiency ratios (if multiple detectors are used) and relative 6.4 The SIMS sodium, aluminum, potassium, and iron
sensitivity factors (RSFs) measured from reference materials. instrumental backgrounds can limit the detection of low levels
of surface metals.
NOTE 1—The discrimination of elemental ions from molecular ions is
27 + 6.5 The accuracy and precision of the measurement can be
particularly important for the Al signal that has a significant interfer-
11 12 2 +
significantly degraded by analysis of specimens whose surfaces
ence below about 10 to 10 atoms/cm from ubiquitous C H
2 3
are not all at the same inclination with respect to the ion
molecular ions that may arise from clean room air or from plastic cassette
containers. The relative importance of the organic interference is depen-
collection optics of the SIMS instrument. The specimen holder
dent upon the surface organics of the test wafer. Another significant
must be constructed and maintained such that after specimen(s)
+
interference occurs from ubiquitous BO when the aluminum is in the
are loaded into the holder, the inclination of the surface of each
9 10 2 12 2
range of 10 to 10 atoms/cm , since surface boron at the 10 atoms/cm
specimen is constant from specimen to specimen.
range is common for all wafers, both n-type as well as p-type. If the
+ 6.6 The accuracy and precision of the measurement signifi-
surface contains high levels of sodium, there may be a NaO molecular
39 + 11 12 + 11 28 +
cantly degrade as the roughness of the specimen surface
interference for K . In principle, B C and B Si can be a
23 + 39 54 +1
molecular interferences for Na and K respectively. The Fe increases. This degradation can be avoided by using chem-
27 +1 54 +1
signal can have interferences from Al or Cr . Discrimination of
2 mechanical polished surfaces.
molecular ion interferences can be achieved using magnetic mass spec-
6.7 If an oxygen leak is not used in conjunction with the
trometers operated under high mass resolution or in some cases using
measurement, there may be a bias due to the effect of different
quadrupole mass spectrometers via energy filters.
chemical native-oxide thicknesses upon ion yields. This effect
has not been studied.
5. Significance and Use
5.1 SIMS can measure on polished silicon wafer product the
7. Apparatus
following:
7.1 SIMS Instrument, equipped with a primary ion beam,
(1) the sodium and potassium areal densities that can affect
+
preferably O , a mass spectrometer with some method of
voltage flatband shifts in integrated circuits, and,
discriminating molecular ion interferences from elemental ions
(2) the aluminum areal density that can affect the thermal
of interest, an electron multiplier detector, or faraday cup
oxide growth rate.
detector, or similar detector system capable of measuring
(3) 3. the iron areal density that can affect gate oxide
secondary ion count rates, or any combination thereof, and the
integrity, minority carrier lifetime, and current leakage.
ability to sputter the surface at less than 0.015 nm/s. An
5.2 The SIMS measurement facilitates the production of
molecular oxygen jet may be used to stabilize the surface ion
silicon wafers with upper control limits on sodium, potassium,
yield; the local oxygen gas flux to the specimen surface must
aluminum, and iron areal densities.
be stable enough that the secondary ion yield does not vary
5.3 This test method can be used for monitoring a mirror-
during the analysis. The stability of the oxygen jet effect can be
polished wafer cleaning process, for research and development,
checked by monitoring a silicon matrix signal during a profile;
and for materials acceptance purposes.
and if the matrix signal is not monitored during a profile, the
5.4 This test method can provide spatial information for
vacuum chamber pressure can be monitored for fluctuations in
these metal contaminants, including near-edge substrate con-
the oxygen gas pressure. The SIMS instrument should be
tamination levels.
adequately prepared and maintained so as to provide the lowest
possible instrumental backgrounds.
6. Interferences
7.2 Test Specimen Holder, reserved for the SIMS measure-
6.1 Surface metal contamination of sodium, aluminum,
ment. In some instruments the holder can support multiple 5 by
potassium or iron introduced during handling of the test
5-mm samples that are held face down against metal (tantalum)
specimen or during the measurement itself will introduce a bias
windows. In other instruments the holder can support one or
more 15 by 15-mm samples by spring clips on the edge of the
specimen or silver paste on the sample back surface. Some
Mollenkopf, H., “Chemicals and Cleanroom Filtered Air Effects on Boron
instruments can hold full silicon wafers. In all cases, the
Contamination and Its Near Surface Detection in Silicon Wafers,” Extended
sample holder should be adequately prepared and maintained
Abstracts, Vol 93-2, Abstract No. 170, The Electrochemical Society, Pennington, NJ,
1993, pp. 273–274.
so as to provide the lowest possible contribution to instrumen-
Frost, M. R., “On the Use of Quadrupole SIMS for the Measurement of Surface
tal backgrounds.
Metallic Contamination,” Contamination Control and Defect Reduction in Semi-
7.3 Stylus Profilometer, or equivalent device (for example,
conductor Manufacturing III, ECS Proceedings, Vol 94-9, edited by D. N. Schmidt,
The Electrochemical Society, Pennington, NJ, 1994, pp. 339–350. atomic force microscope) to measure SIMS crater depths. This
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 1617 – 98 (2002)
is required to calibrate depth scales for concentration profiles 10.1.1 Reference materials may be either:
of calibration standard samples. For routine depth scale cali-
10.1.1.1 Spin Coat Contaminated Samples, calibrated by
bration of test specimens, the instrument must be capable of
Vapor Phase Decomposition/Atomic Absorption Spectroscopy
crater depth measurements of 10 nm with an accuracy and
(VPD/AAS) or Vapor Phase Decomposition/Inductively-
precision of 10 %. In the absence of such an instrument, a
Coupled-Plasma Mass Spectrometry (VPD/ICP-MS) and
secondary depth calibration standard (such as a silicon wafer
shown by qualitative SIMS to be spatially uniform, since
with a known impurity depth profile) must be prepared and can
spatial non-uniformity can introduce variability or bias to the
be used to measure the SIMS sputter rate during the measure-
SIMS quantitative measurement. With a spin coat contami-
ment.
nated reference sample, it may be possible to avoid the need for
the crater depth measurement and its bias/variability. For this
NOTE 2—The accurate measurement of sputter crater depths on the
reference sample the areal density D in (Eq 1) (see 12.1) is the
order of and below 10 nm is still an area of research, because the sputtered
silicon is very reactive to oxygen in the air when removed from the SIMS elemental areal density determined by the VPD/AAs or VPD/
chamber for crater depth measurement. For example, sputter craters
ICP-MS, corrected for isotopic abundance since the SIMS
expected to be only 1 nm in depth can actually be thicker than the original
measurement of SI is isotopic.
i
native oxide due to this rapid oxide growth on sputtered silicon, that is,
10.1.1.2 Silicon Wafers, dipped in an intentionally contami-
one observes a bump on the surface where the erosion was, rather than a
nated SC-1 (NH OH:H O :H O) bath where the calibration of
crater. If a reference sample is similar to the unknown in type, that is, 4 2 2 2
the metal deposition is by VPD/AAS or VPD/ICP-MS and
intentional surface contamination rather than shallow ion implant, it may
be possible to avoid the need for a direct shallow crater depth measure-
shown by qualitative SIMS, or by TXRF for iron, to be
ment on each sample.
spatially uniform, since spatial non-uniformity can introduce
variability or bias to the SIMS quantitative measurement. With
8. Sampling
an SC-1 dipped reference sample, it may be possible to avoid
8.1 Since this procedure is destructive in nature, a sampling
the need for the crater depth measurement and its bias/
procedure must be used to evaluate the characteristics of a
variability. For this reference sample the areal density D in (Eq
group of silicon wafers. No general sampling procedure is
1) is the elemental areal density determined by the VPD/AAS
included as part of this test method, because the most suitable
or VPD/ICP-MS, corrected for isotopic abundance since the
sampling pl
...
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