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SEMI MF1188-0305 © SEMI 2003, 2005 3 3 Limitations 3.1 The oxygen absorption band overlaps a silico n lattice band. The oxygen-free reference specimen must be matched within ±0.5% to the thickn ess of the test specimen i…
SEMI MF1188 © SEMI 2003, 2005 2
Despite the fact that IOC-88 has been adopted by all of the major standards developing
organizations active in the semiconductor field, many older calibration factors that have been used
in earlier standards issued by ASTM and other standards development organizations are still in use
in the industry today. Tables showing the relations between the IOC-88 interstitial oxygen
calibration factor and other standardized calibration factors that have been used in the silicon
semiconductor industry can be found in SEMI M44. It should be emphasized that these factors are
at times referred to in the literature by common names and at other times by the designation of the
standard where they were used. Furthermore, in the jargon of the industry, interstitial oxygen
content is frequently described as being determined in accordance with a particular standardized
method whereas, in actual fact, only the calibration factor is taken from the standard while the
measurement itself is made by whatever method is employed within the instrumentation used.
1 Purpose
1.1 The presence of oxygen can be beneficial to certain manufacturing operations by preventing the formation of
process-induced defects. Oxygen is introduced into silicon wafers during the crystal growing process. Hence, it is
important to control the oxygen content of silicon crystals.
1.2 Measurement of the intensity of the 1107 cm
1
oxygen-in-silicon band with an infrared spectrophotometer
enables the determination of the value of the absorption coefficient and, hence, by the use of a calibration factor or
linear regression curve, the content of interstitial oxygen.
1.3 This test method can be used as a referee method for determining the interstitial oxygen content of silicon slices.
Knowledge of the interstitial oxygen content of silicon wafers is necessary for materials acceptance and control of
fabrication processes, as well as for research and development.
2 Scope
2.1 This test method covers the determination of the interstitial oxygen content of single crystal silicon by
measurement of an infrared absorption band at room temperature. This test method requires the use of an oxygen-
free reference specimen. It is recommended that a reference material set, such as NIST SRM
3
2551,
4
another
certified reference material set for oxygen content of silicon,
6
or reference materials traceable to the CRMs, be used
to calibrate the spectrophotometer in order to reduce bias.
2.2 This test method requires the use of a computerized spectrophotometer, preferably a Fourier Transform Infrared
(FT-IR) spectrophotometer. This method is incorporated into many modern FT-IR instruments.
2.3 The useful range of oxygen concentration measurable by this test method is from 1 × 10
16
atoms/cm
3
to the
maximum amount of interstitial oxygen soluble in silicon.
2.4 If the spectrophotometer is calibrated using 2 mm thick double-side polished CRMs, this test method is suitable
for use only with 2 mm thick, double-side polished test specimens. It can be extended to the measurement of test
specimens polished on one or both sides with thickness in the range 0.4 mm to 4 mm with the use of working
reference materials traceable to the double-side polished CRMs.
2.5 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.
NOTICE: This standard does not purport to address safety issues, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate safety and health guides and determine the
applicability of regulatory or other limitations prior to use.
6 In addition to NIST SRM 2551 (Office of Standard Reference Materials, National Institute of Standards and Technology, 100 Bureau Drive,
Gaithersburg, MD 20899-2322), certified reference materials for measurements of the interstitial oxygen content of silicon can be obtained from
JEITA (see footnote 12) and from BCR (CRM 368 and CRM 369, from the Community Bureau of Reference, Commission of the European
Communities, rue de la Loi 200, B-1040 Brussels, Belgium).
SEMI MF1188-0305 © SEMI 2003, 2005 3
3 Limitations
3.1 The oxygen absorption band overlaps a silicon lattice band. The oxygen-free reference specimen must be
matched within ±0.5% to the thickness of the test specimen in order to properly remove the effects of the silicon
lattice absorption.
3.2 Since both the oxygen band and the lattice band can change with the specimen temperature, the temperature
inside the spectrophotometer sample compartment must be maintained at 27 ± 5°C during the measurement.
3.3 Significant free carrier absorption occurs in n-type silicon with resistivity below 1 ·cm, and in p-type silicon
with resistivity below 3.0 ·cm. For test specimens below these resistivities, the reference crystal must be matched
in resistivity as well as in thickness. The resistivity match must be sufficiently close so that the transmittance of the
test specimen relative to the reference specimen at 1600 cm
1
must be 100 ± 5 %.
3.4 The free carrier absorption in n-type crystals with resistivities less than 0.1 ·cm, or in p-type crystals with
resistivities less than 0.5 ·cm reduces the available energy below that required for the satisfactory operation of
most spectrophotometers.
3.5 The full width at half maximum (FWHM) of the oxygen-in-silicon band at 300 K is 32 cm
1
. Calculations
made from spectral data having a FWHM greater than this value may be in error.
4 Referenced Standards
4.1 SEMI Standards
SEMI C29 — Specifications and Guideline for 4.9% Hydrofluoric Acid 10:1 v/v
SEMI M44 — Guide to Conversion Factors for Interstitial Oxygen in Silicon
4.2 ASTM Standards
E 1 — Specification for ASTM Thermometers
7
E 131 — Terminology Relating to Molecular Spectroscopy
8
E 932 — Practice for Describing and Measuring Performance of Dispersive Infrared Spectrophotometers
8
F 121— Test Method for Intersititial Atomic Oxygen Content of Silicon by Infrared Absorption
9
4.3 JEITA (formerly JEIDA) Standard
EM-3504 (61) — Standard Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption
10
4.4 DIN Standard
50438/1 — Determination of Impurity Content in Silicon by Infrared Absorption: Oxygen
11
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 For definitions of terms relating to absorption spectroscopy, refer to ASTM Terminology E 131.
5.2 Definitions
7 Annual Book of ASTM Standards, Vol 14.03, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Telephone: 610-
832-9500, Fax: 610-832-9555, Website:
www.astm.org
8 Annual Book of ASTM Standards, Vol 03.06.
9 Withdrawn in 1988; last available edition in the 1987 edition of Annual Book of ASTM Standards, Vol 10.05.
10 Japan Electronics and Information Technology Industries Association, 3
rd
floor, Mitsui Sumitomo Kaijo Bldg. Annex, 11, Kanda-Surugadai
3-chome, Chiyoda-ku, Tokyo 101-0062, Japan, Website:
www.jeita.or.jp
.
11 Deutches Institut für Normung e.V., standards are available in both English and German editions from Beuth Verlag GmbH,
Burggrafenstrasse 6, 10787 Berlin, Germany, Telephone: 49.30.2601-0, Fax: 49.30.2601.1263, Website:
www.din.de
.
SEMI MF1188 © SEMI 2003, 2005 4
5.2.1 certified reference material (CRM), n — a reference material, one or more of whose property values are
certified by a technically valid procedure, accompanied by or traceable to a certificate or other documentation issued
by a certifying body.
5.2.2 dispersive infrared (DIR) spectrophotometer, n — a type of infrared spectrometer that uses at least one prism
or grating as the dispersing element, in which the data are obtained as an amplitude-wavenumber (or wavelength)
spectrum.
5.2.2.1 Discussion — Some dispersive infrared spectrometers are used in conjunction with a computer, which is
used to store data. The data are then accessible for manipulation or computation, as required. These spectrometers
are referred to as computer-assisted dispersive infrared spectrophotometers (CA-DIR). Dispersive infrared
spectrometers that are not computer-assisted are referred to, for convenience, as simple dispersive infrared
spectrometers (S-DIR).
5.2.3 Fourier transform infrared (FT-IR) spectrophotometer, n — a type of infrared spectrometer in which the data
are obtained as an interferogram.
5.2.3.1 Discussion — An interferogram is a record of the modulated component of the interference signal measured
by the detector as a function of retardation in the interferometer. This interferogram is then subjected to a Fourier
transformation to obtain an amplitude-wavenumber (or wavelength) spectrum. Due to the complexity of the Fourier
transformation, FT-IR instruments are always used in conjunction with a computer.
5.2.4 reference spectrum, n — the spectrum of the reference specimen.
5.2.4.1 Discussion — In true double-beam spectrometers, the reference spectrum may be obtained directly, with the
reference specimen in the sample beam, and the reference beam empty. In single-beam spectrometers, it can be
calculated from the ratio of a spectrum obtained with the reference specimen in the IR beam, to a background
spectrum.
5.2.5 sample spectrum, n — the spectrum of the test specimen.
5.2.5.1 Discussion — In true double-beam spectrometers, the sample spectrum may be obtained directly, with the
sample specimen in the sample beam, and the reference beam empty. In single-beam spectrometers, it can be
calculated from the ratio of a spectrum obtained with the test specimen in the IR beam, to a background spectrum.
6 Summary of Test Method
6.1 The relative infrared transmittance spectrum of an oxygen-containing silicon slice is obtained using a reference
method with a calibrated IR spectrophotometer, preferably one calibrated by means of a suitable set of reference
materials. The oxygen-free reference specimen is matched closely in thickness to the test specimen, so as to
eliminate the effects of absorption due to silicon lattice vibrations.
6.2 After conducting selected instrumental checks, the infrared transmittance spectrum is measured over the
wavenumber range from 900 cm
1
to 1300 cm
1
.
6.3 The measured absorption coefficient of the 1107 cm
1
oxygen-in-silicon band is then used to determine the
interstitial oxygen content of the silicon slice.
7 Apparatus
7.1 Infrared Spectrophotometer , either a DIR (S or CA), or FT-IR instrument, as described in ¶5.2.2 and ¶5.2.3,
respectively, may be used. It must be possible to set the resolution of the spectrophotometer to 4 cm
1
, or better, for
FT-IR spectrophotometers, and to 5 cm
1
, or better, for DIR spectrophotometers. Use of an FT-IR spectropho-
tometer is strongly recommended.
7.2 The three following paragraphs apply only to FT-IR spectrophotometers:
7.2.1 Zero Filling — When an FT-IR instrument collects an unsymmetrical interferogram, an additional set of
points whose values are all zero shall be added to the end of the collected interferogram such that the total number of
points for performing the Fourier transform is double the number of data points originally collected.
7.2.2 Undersampling — The data collection method shall produce interferograms which, when zero-filled and
Fourier transformed, produce a spectrum containing at least two data points per resolution increment. For example,