ASTM F1188-00
(Test Method)Standard Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption
Standard Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption
SCOPE
1.1 This test method covers the determination of the interstitial oxygen content of single crystal silicon by infrared spectroscopy. This test method requires the use of an oxygen-free reference specimen and a set of calibration standards, such as those comprising NIST SRM 2551. It permits, but does not require, the use of a computerized spectrophotometer.
1.2 The useful range of oxygen concentration measurable by this test method is from 1 X 1016 atoms/cm3 to the maximum amount of interstitial oxygen soluble in silicon.
1.3 The oxygen concentration obtained using this test method assumes a linear relationship between the interstitial oxygen concentration and the absorption coefficient of the 1107 cm-1 band associated with interstitial oxygen in silicon.
1.4 This standard does not purport to address all of the safety problems, 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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: F 1188 – 00
Standard Test Method for
Interstitial Atomic Oxygen Content of Silicon by Infrared
Absorption
This standard is issued under the fixed designation F 1188; 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 oxygen concentration and the absorption coefficient of the 1107
−1
cm band associated with interstitial oxygen in silicon.
1.1 This test method covers the determination of the inter-
1.4 This standard does not purport to address all of the
stitial oxygen content of single crystal silicon by infrared
2, 3, 4, 5, 6, 7
safety concerns, if any, associated with its use. It is the
spectroscopy. This test method requires the use of an
responsibility of the user of this standard to establish appro-
oxygen-free reference specimen and a set of calibration stan-
8,9
priate safety and health practices and determine the applica-
dards, such as those comprising NIST SRM 2551. It permits,
bility of regulatory limitations prior to use.
but does not require, the use of a computerized spectropho-
tometer.
2. Referenced Documents
1.2 The useful range of oxygen concentration measurable
16 3 2.1 ASTM Standards:
by this test method is from 1 3 10 atoms/cm to the
E 1 Specification for ASTM Thermometers
maximum amount of interstitial oxygen soluble in silicon.
E 131 Terminology Relating to Molecular Spectroscopy
1.3 The oxygen concentration obtained using this test
E 932 Practice for Describing and Measuring Performance
method assumes a linear relationship between the interstitial
of Dispersive Infrared Spectrophotometers
1 3. Terminology
This test method is under the jurisdiction of ASTM Committee F01 on
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon
3.1 For definitions of terms relating to absorption spectros-
Materials and Process Controls.
copy, refer to Terminology E 131.
Current edition approved June 10, 2000. Published August 2000. Originally
3.2 Definitions:
published as F 1188 – 88. Last previous edition F 1188 – 93a.
ASTM Test Method F 121 (editions of 1980 through 1983, replaced by Test
3.2.1 dispersive infrared (DIR) spectrophotometer, n—a
Method F 1188 in 1988).
type of infrared spectrometer that uses at least one prism or
DIN 50438, Part 1 (edition of 1973, revised to cite IOC-88 in 1995), DIN
grating as the dispersing element, in which the data are
50438, Part 1 (1995) is referred to in Tables X1.1 and X1.2.
obtained as an amplitude-wavenumber (or wavelength) spec-
Iizuka, T., Takasu, S., Tajima, M., Arai, T., Nozaki, T., Inoue, N., and Watanabe,
M., “Determination of Conversion Factor for Infrared Measurement of Oxygen in
trum.
Silicon,” Journal of the Electrochemical Society, Vol 132, 1985, pp. 1707–1713.
3.2.1.1 Discussion—Some dispersive infrared spectrom-
JEDIA standard 61-2000 (Standard Test Method for Atomic Oxygen Content of
eters are used in conjunction with a computer, which is used to
Silicon by Infrared Absorption) issued in 2000, cites I0C-88.
Old edition; cited in Reference 6. Since revised to cite I0C–88. store data. The data are then accessible for manipulation or
Baghdadi, A., Bullis, W. M., Coarkin, M. C., Li Yue-zhen, Scace, R. I., Series,
computation, as required. These spectrometers are referred to
R. W., Stallhofer, P., and Watanabe, M., “Interlaboratory Determination of the
as computer-assisted dispersive infrared spectrophotometer
Calibration Factor for the Measurement of the Interstitial Oxygen Content of Silicon
(CA-DIR). Dispersive infrared spectrometers that are not
by Infrared Absorption,” Journal of the Electrochemical Society, Vol 136, 1989, pp.
2015–2034.
computer-assisted are referred to, for convenience, as simple
ASTM Test Method F 121 (editions of 1970 through 1979).
dispersive infrared spectrometers (S-DIR).
SRM 2551, available from the National Institute of Standards and Technology,
3.2.2 Fourier transform infrared (FT-IR) spectrophotom-
Gaithersburg, MD 20899 USA, has been found to be suitable for this purpose.
eter, n—a type of infrared spectrometer in which the data are
DIN 50438 Part 1 is similar to, but more general than, this test method. It
includes two methods: Method A, which is restricted to double side polished or
obtained as an interferogram.
polish-etched wafers, and Method B, which is applicable to wafers with one side
3.2.2.1 Discussion—An interferogram is a record of the
polished and one side etched for wafers as thin as 0.03 cm. DIN 50438 Part 1 is
modulated component of the interference signal measured by
intended for use with computer aided spectrophotometers, whether dispersive or
FTIR. It is the responsibility of DIN Committee NMP 221 with which ASTM F-1 the detector as a function of retardation in the interferometer.
maintains close liason. DIN 50438 Part 1, Determination of Impurity Content in
Semiconductors by Infrared Absorption, Oxygen in Silicon, may be obtained from
Beuth Verlag GmbH, Berggrafenstrasse 4-10, D-1000 Berlin 30, Germany (see also
the Related Material Section of the 1993 edition of the Annual Book of ASTM Annual Book of ASTM Standards, Vol 14.03.
Standards, Vol 10.05). 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 1188–00
This interferogram is then subjected to a Fourier transforma- with a resistivity below 3.0 V·cm. For test specimens below
tion to obtain an amplitude-wavenumber (or wavelength) these resistivities, the reference crystal must be matched in
spectrum. Due to the complexity of the Fourier transformation, resistivity as well as in thickness. The resistivity match must be
FT-IR instruments are always used in conjunction with a sufficiently close so that the transmittance of the test specimen
−1
computer. relative to the reference specimen at 1600 cm must be 1006
3.2.3 reference spectrum, n—the spectrum of the reference 5%.
specimen. 6.4 The free carrier absorption in n-type crystals with
3.2.3.1 Discussion—In true double-beam spectrometers, it resistivities less than 0.1 V·cm, or in p-type crystals with
may be obtained directly, with the reference specimen in the resistivities less than 0.5 V·cm reduces the available energy
sample beam, and the reference beam empty. In single-beam below that required for the satisfactory operation of most
spectrometers, it can be calculated from the ratio of a spectrum spectrophotometers.
obtained with the reference specimen in the IR beam, to a 6.5 The presence of a high concentration of oxide precipi-
−1
background spectrum. tates, that result in absorbance bands at 1230 cm or 1073
−1
3.2.4 sample spectrum, n—the spectrum of the test speci- cm , may lead to an error in the interstitial oxygen determi-
men. nation.
3.2.4.1 Discussion—In true double-beam spectrometers, it 6.6 The full width at half maximum (FWHM) of the
−1
may be obtained directly, with the sample specimen in the oxygen-in-silicon band at 300 K is 32 cm . Calculations
sample beam, and the reference beam empty. In single-beam made from spectral data having a FWHM greater than this
spectrometers, it can be calculated from the ratio of a spectrum value will be in error.
obtained with the test specimen in the IR beam, to a back-
7. Apparatus
ground spectrum.
7.1 Infrared spectrophotometer, either a S-DIR, CA-DIR or
4. Summary of Test Method FT-IR instrument, as described in 3.2.1 and 3.2.2 may be used.
It must be possible to set the resolution of the spectrophotom-
4.1 The relative infrared transmittance spectrum of an
−1
eter to 4 cm , or better, for Fourier transform infrared
oxygen-containing silicon slice, which is mirror-polished on
−1
spectrophotometers, and to 5 cm , or better, for dispersive
both sides, is obtained using a reference method with an IB
spectrophotometers.
spectrophotometer calibrated by means of a suitable set of
7.2 The three following paragraphs apply only to FT-IR
reference materials. The oxygen-free reference specimen is
spectrophotometer:
matched closely in thickness to the test specimen, so as to
7.2.1 Zero Filling—When an FT-IR instrument collects an
eliminate the effects of absorption due to silicon lattice
−1
unsymmetrical interferogram, an additional set of points whose
vibrations. The absorption coefficient of the 1107 cm
values are all zero shall be added to the end of the collected
oxygen-in-silicon band is then used to calculate the interstitial
interferogram such that the total number of points for perform-
oxygen content of the silicon slice.
ing the Fourier transform is double the number of data points
originally collected.
5. Significance and Use
7.2.2 Undersampling—The data collection method shall
−1
5.1 Measurement of the intensity of the 1107 cm oxygen-
produce interferograms which, when zero-filled and Fourier
in-silicon band with an infrared spectrophotometer enables the
transformed, product a spectrum containing at least two data
determination of the value of the absorption coefficient and,
points per resolution increment. For example, after transfor-
hence, by the use of a conversion coefficient, the content of
−1
mation, a spectrum obtained at 4 cm resolution shall contain
interstitial oxygen.
at least one data point every two wavenumbers.
5.2 This test method can be used as a referee method for
7.2.3 Phase Correction—The phase correction routine used
determining the interstitial oxygen content of silicon slices
during Fourier transformation shall use at least 200 points on
which are polished on both sides. Knowledge of the interstitial
both sides of the point of zero retardation in order to produce
oxygen content of silicon wafers is necessary for materials
a phase array that can be used to eliminate phase errors.
acceptance and control of fabrication processes, as well as for
7.3 Specimen Holders of Appropriate Size—If the test
research and development.
specimen is small, it must be mounted in a holder that has an
opening small enough to prevent any of the infrared beam from
6. Interferences
bypassing the specimen. The specimens shall be held normal,
6.1 The oxygen absorption band overlaps a silicon lattice
or nearly normal, to the axis of the incident infrared beam (see
band. The oxygen-free reference specimen must be matched
8.3).
within 60.5 % to the thickness of the test specimen in order to
7.4 Equipment and Materials, for slicing and polishing
properly remove the effects of the silicon lattice absorption.
crystals to a thickness similarity of 0.5 % or less and a surface
6.2 Since both the oxygen band and the lattice band can
flatness equal to one fourth the wavelength at the maximum
change with the specimen temperature, the temperature inside
absorption of the impurity band under study.
the spectrophotometer sample compartment must be main-
tained at 27 6 5°C during the measurement.
6.3 Significant free carrier absorption occurs in n-type 12
For a discussion of the phase correction computation, see Chase, D. B.,
silicon with a resistivity below 1 V·cm, and in p-type silicon Applied Spectroscopy, Vol 36, 1982, p. 240.
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 1188–00
the optical thickness of the specimen. These fringes can obscure a weak
7.5 Micrometer Caliper, or other instrument suitable for the
spectral line and prevent accurate measurement of the baseline. To prevent
measurement of the thickness of the specimens to a tolerance
obscuration by these interference fringes, nonparallel specimen surfaces
of 60.2 %.
may be a necessity.
7.6 Thermocouple-Millivolt Potentiometer, or other system
NOTE 2—However, the use of specimens with nonparallel surfaces can
suitable for measurements of the specimen temperature during
also result in photometric errors. If a material has a high refractive index,
test.
any nonparallelism of the specimen can displace the spectrometer beam
relative to the active area of the detector. The same effect can occur even
8. Testing of the Apparatus
with a thin specimen in a cryogenic system if the specimen is not
cemented properly or the holder plate twists. Thus, a lowered transmission
8.1 Evaluate the performance of S-DIR spectrometers ac-
occurs. Improper positioning or nonparallelism of the specimen can be
cording to Instrument Operation Section, and Nature of Test
checked by rotating the specimen to determine whether the transmission
Sections of Practice E 932. Follow the appropriate paragraphs
level stays constant. Any variation is a possible indication of problems
of these sections to evaluate the performance of CA-DIR
with the specimen positioning or preparation.
instruments.
9.3 Since a difference technique is used in this test method,
8.2 Verify a proper purge condition for the specimen cham-
prepare a reference specimen of the same type of material as
ber by monitoring water vapor or carbon dioxide absorption
−1 the sample, but chosen to be free of oxygen (see 9.3.1). The
bands. The water vapor line is monitored at 1521 cm and the
reference crystal must be prepared to the same tolerances as the
−1
carbon dioxide line at 667 cm . The instrument shall be
test specimen. The thickness of the reference specimen shall be
sufficiently well purged or evacuated that the transmittance at
equal to that of the test specimen to within6 0.5 %.
these locations is between 98 and 102 %.
9.3.1 Choose the reference specimen from slices taken from
8.3 Under certain conditions, the spectrophotometer may
five to ten different crystals that are thought to be free of
have a nonlinear response, or be plagued by undesirable
oxygen. Compare these slices with one another and choose the
extraneous reflections between the specimen surfaces and the
specimen with the lowest absorption as the reference specimen.
spectrometer components. Place a flat, double-side polished
If no absorption is seen for any of the specimens, then the
and high resistivity (greater than 5V· cm) silicon slice in the
assumption can be made that all specimens contain less than
instrument. The effective transmittance of the silicon slice, due
the limit of detection of oxygen and any of the specimens can
to reflective losses at the silicon surfaces, should be 53.8 6
be used as the refer
...
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