ASTM F1619-95(2000)e1

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.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.
e1
Designation: F 1619 – 95 (Reapproved 2000)
Standard Test Method for
Measurement of Interstitial Oxygen Content of Silicon
Wafers by Infrared Absorption Spectroscopy with
p-Polarized Radiation Incident at the Brewster Angle
This standard is issued under the fixed designation F 1619; 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.
e NOTE—Editorial changes were made throughout in April 2002.
1. Scope derived directly using an independently determined calibration
factor.
1.1 This test method covers determination of the absorp-
1.3 The test specimen is a single-side polished silicon wafer
tion coefficient due to the interstitial oxygen content of
of the type specified in SEMI Specifications M1. The front
commercial monocrystalline silicon wafers by means of Fou-
surface of the wafer is mirror polished and the back surface
rier transform infrared (FT-IR) spectroscopy. In this test
may be as-cut, lapped, or etched (see 8.1.1.1).
method, the incident radiation is p-polarized and incident on
1.4 This test method is applicable to silicon wafers with
the test specimen at the Brewster angle in order to minimize
resistivity greater than 5 V·cm at room temperature.
multiple reflections.
1.5 This standard does not purport to address all of the
NOTE 1—In this test method, radiation in which the electric vector is
safety concerns, if any, associated with its use. It is the
parallel to the plane of incidence is defined as p-polarized radiation.
responsibility of the user of this standard to establish appro-
NOTE 2—Committee F01 has been advised that some aspects of this test
priate safety and health practices and determine the applica-
method may be subject to a patent applied for by Toshiba Ceramics
bility of regulatory limitations prior to use.
Corporation. The Committee takes no position with respect to the
applicability or validity of such patents, but it requests users of this test
2. Referenced Documents
method and other interested parties to supply any information available on
non-patented alternatives for use in connection with this test method.
2.1 ASTM Standards:
F 1188 Test Method for Interstitial Atomic Oxygen Content
1.2 Since the interstitial oxygen concentration is propor-
−1
of Silicon by Infrared Absorption
tional to the absorption coefficient of the 1107 cm absorption
F 1241 Terminology of Silicon Technology
band, the interstitial oxygen content of the wafer can be
2.2 SEMI Standard:
SEMI M1 Specifications for Polished Monocrystalline
Silicon Wafers
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. Terminology
Materials and Process Control.
Current edition approved Sept. 15, 1995. Published November 1995.
3.1 Definitions of terms related to silicon technology are
This standard is based on draft procedures and interlaboratory tests conducted
found in Terminology F 1241.
by the Silicon Wafer Committee of the SEMI Japan Standards Program and the
3.2 Definitions of terms related specifically to FT-IR spec-
Oxygen and Carbon Measurement Committee of the Japan Electronic and Informa-
troscopy are found in Test Method F 1188.
tion Technology Industries Association (JEITA), 3rd Floor Mitsui Kaijo Bldg.
Annex 11, Kanda Surugadai 3–chome, Chiyoda-Ku, Tokyo, 101–0062, Japan.
Krishnan, K., “Precise and Rapid Measurement of Oxygen and Carbon in
4. Summary of Test Method
Silicon,” Defects in Silicon, edited by W. M. Bullis and L. C. Kimerling,
4.1 The stability of the FT-IR spectrometer is established to
Proceedings Volume 83-9, The Electrochemical Society, Pennington, NJ, 1983, pp.
285–292; Shirai, H., “Determination of Oxygen Concentration in Single-Side be adequate for the measurement cycle.
Polished Czochralski-Grown Silicon Wavers by p-Polarized Brewster Angle Inci-
4.2 The optimum angle of incidence is determined to
dence Infrared Spectroscopy,” Journal of The Electrochemical Society, Vol 138, No.
minimize multiple internal reflection.
6, 1991, pp. 1784–1787; Shirai, H., “Oxygen Measurements in Acid-Etched
4.3 The transmission spectrum of an oxygen-free double-
Czochralski-Grown Silicon Wafers,” Journal of The Electrochemical Society,Vol
139, No. 11, 1992, pp. 3272–3275.
side polished float-zone wafer is recorded.
“Measuring Method of Interstitial Oxygen Content of Silicon Wafers,” U.S.
Patent applied for. Information concerning use of the concepts covered by this patent
application and its state of issuance may be obtained from Intellectual Property
Department, Toshiba Ceramics Co., Ltd., Shinjuku Nomura Building, 26-2 Nishi- Annual Book of ASTM Standards, Vol 10.05.
Shinjuku, 1-Chome, Shinjuku-ku, Tokyo 163-05, Japan, Facsimile + 81-3-3343- Available from Semiconductor Equipment and Materials International, 3081
8627. Zanker Rd., San Jose, CA 95134 (www.semi.org).
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 1619
4.4 The transmission spectrum of the oxygen-containing 6.5 Reference Wafer is required in order to determine the
test specimen is determined. absorption due to the silicon lattice spectrum at the wavenum-
4.5 The negative logarithm of each of these transmission ber of the peak of the oxygen absorption.
spectra is taken to determine the absorbance spectra. 6.6 Temperature Control—Since both oxygen and silicon
4.6 The absorbance spectra are normalized by dividing by lattice absorption change with temperature, the temperature
the beam path length to obtain the absorption coefficient as a inside the spectrometer chamber must be maintained at 27 6
function of wavenumber. 5°C during the measurement as required by Test Method
4.7 The baseline is corrected for curvature resulting from F 1188.
scattering from the rough back surface and the baseline value 6.7 Nonlinearity in the spectrometer and its detecting
−1
at 1107 cm is determined. system can degrade the accuracy of the measurement.
4.8 This baseline value is subtracted from the absorbance at
7. Apparatus
−1
1107 cm to determine the absorption coefficient due to
7.1 Single-Beam Fourier Transform Infrared Spectrometer,
interstitial oxygen.
as specified in Test Method F 1188, capable of collecting
4.9 The absorption coefficient is multiplied by the appropri-
−1
transmission spectra with resolution of both 4 cm and 1
ate calibration factor to obtain the oxygen content of the test
−1
cm .
specimen.
7.2 Polarizer, in order that the incident beam shall be
p-polarized.
5. Significance and Use
7.3 The central angle of the incident beam flux shall be
5.1 Control of the oxygen content is essential for silicon
adjustable between 65° and 75° from the surface normal.
wafers to be used for advanced devices and integrated circuits.
7.4 Detector shall be large enough that the shifting of the
It is desirable to be able to measure the oxygen content of
beam by the sample (a lateral distance equal to 0.88 times the
product wafers, nondestructively and without regard for back
sample thickness) does not affect its sensitivity. Detector
surface finish. This test method provides a means for reducing
sensitivity shall be unchanged whether a sample is or is not in
the influence of the back surface condition on the measure-
the measurement beam.
ment.
5.2 This test method may be used for routine process 8. Test and Reference Specimens
monitoring, quality control, materials acceptance, and research
8.1 Test Specimen:
and development.
8.1.1 A silicon wafer with chem-mechanically polished
front surface and a back surface that may be as-cut, lapped or
6. Interferences
etched. The back-surface roughness shall be such that:
6.1 Multiple Reflections are greatest for thin, double-side
8.1.1.1 The rms roughness shall be less than 0.9 μm,
−1
polished wafers with parallel front and back surfaces. In this
8.1.1.2 The transmittance through the wafer at 1107 cm
case, the transmittance, T, is given as follows:
shall equal or exceed 25 %, or
2 2ax
8.1.1.3 The difference between the absorption coefficient at
~1 2 R! e
2 2ax 2 22ax 4 24ax
−1 −1
T 5 5 ~1 2 R! e @1 1 R e 1 R e 1 .#
2 22ax
1200 cm and the absorption coefficient at 950 cm shall be
1 2 R e
−1
positive but less than 5 cm .
(1)
8.1.2 Wafers shall have thickness in the range specified in
where:
SEMI Specifications M1 (between 500 and 750 μm for wafers
R = reflectance ratio,
with diameter from 100 to 200 mm). Measure and record as
−1
a = absorption coefficient in cm , and
d the thickness of each test specimen to the nearest μm.
CZ
x = optical path length in cm ( = dcosu , where
r
8.1.3 The resistivity of either n-or p-type test specimens
d = specimen thickness, in cm, and u = angle of
r
shall be greater than 5 V·cm.
refraction (see 10.1).
8.2 Oxygen-Free Reference Specimen:
2 −2ax
To neglect multiple reflections, the quantity R e should be
8.2.1 A double-side polished, float-zoned silicon wafer with
less than 0.001. The reflection is suppressed for incident 16 3
maximum oxygen content of 1 3 10 atoms/cm (0.2 ppma)
radiation at the Brewster angle (73.7° from the normal in
and resistivity greater than 5 V·cm.
silicon). However, because of the large cone angle of the
8.2.2 Measure and record as d the thickness to the nearest
FZ
incident radiation in FT-IR spectrometers with focused beam
μm; the thickness of the reference specimen shall be within
not all of the radiation is precisely at the Brewster angle.
620 % of that of the test specimen.
Procedures to minimize this effect are given in 9.2.
8.3 A second double-side polished, float-zoned wafer, ;400
6.2 Optical Path Length of the transmitted beam is esti-
μm thick, for use in determining the optimum angle of
mated from the central beam angle of the incident non-parallel
incidence.
beam flux.
8.4 Sapphire wafer $400 μm-thick, polished on one or both
6.3 Surface Scattering—the baseline that is due largely to
sides.
surface scattering is approximated by a parabolic curve (see
9. Procedure
Appendix X1).
6.4 Free Carrier Absorption is minimized by requiring that 9.1 Determine Stability of FT-IR Spectrometer:
the resistivity of the test and reference specimens be greater 9.1.1 Turn on the spectrometer and allow it to operate long
than 5 V·cm. enough to stabilize.
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 1619
−1
9.1.2 Set the resolution of the spectrometer to 4 cm . fringes in the spectrum; the magnitude should decrease as the
9.1.3 Use a minimum of 64 scans for each spectrum angle of incidence approaches the Brewster angle.
collection.
9.2.2.4 Repeat 9.2.2.3, decreasing the angle of incidence
9.1.4 100 % Line Check:
each time until the magnitude of the interference fringes begins
9.1.4.1 Collect a background spectrum I (v) with the
to increase.
sample beam empty over the wavenumber range from 900 to
9.2.2.5 Record, to the nearest 1°, the angle of incidence for
−1
1300 cm .
the minimum fringe magnitude as u .
iFM
9.1.4.2 Wait a time interval, t minutes, long enough to make
9.2.3 Single Beam Maximum (SBM) Method:
−1
the desired measurements on the test and reference specimens,
9.2.3.1 Set the resolution of the spectrometer to 4 cm .
and then again collect a background spectrum I (v) with the
9.2.3.2 Adjust the angle of the specimen holder so that the
sample beam empty over the wavenumber range from 900 to
angle of incidence to a value somewhat larger than the
−1
1300 cm . The time interval t shall be at least 60 min.
Brewster angle, and measure the intensity transmitted at 1107
−1
9.1.4.3 Determine the ratio I (v)/I (v) over the wavenum-
01 02
cm with the thin, double-side polished, float-zoned wafer
−1
ber range from 900 to 1300 cm .
(see 8.3) in the sample beam.
9.1.4.4 If the ratio I (v)/I (v) = 1.000 6 0.005 (100.0 6
01 02
9.2.3.3 Rotate the specimen holder so that angle of inci-
0.5 %) over the entire wavenumber range, the instrument is
dence is decreased by 1° and again measure the intensity
−1
acceptable for use in any measuring sequence that requires a
transmitted at 1107 cm with the thin double-side polished
total elapsed time #t minutes.
float-zoned wafer in the sample beam; the intensity should
9.1.4.5 If the ratio I (v)/I (v) falls outside the range 1.000
01 02
increase as the angle of incidence approaches the Brewster
6 0.005 in any part of the wavenumber range 900 to 1300
angle.
−1
cm , reduce the time interval, t, and repeat 9.1.4.1-9.1.4.4
9.2.3.4 Repeat 9.2.3.3, decreasing the angle of incidence
until the ratio I (v)/I (v) = 1.000 6 0.005 over the entire
−1
01 02
each time until the transmitted intensity at 1107 cm begins to
wavenumber range.
decrease.
9.1.4.6 Ensure that any sequence of measurements made
9.2.3.5 Record, to the nearest 1°, the angle of incidence for
using a single background spectrum is completed within the
−1
the maximum transmitted intensity at 1107 cm as u .
isBM
time interval t minutes.
9.3 Collect a background spectrum I over the wavenumber
9.1.5 0 % Line Check:
−1
range from 900 to 1300 cm with the sample beam empty.
9.1.5.1 Collect a background spectrum I (v) with the sample
Collect this and all subsequent spectra with a minimum of 64
beam empty over the wavenumber range from 900 to 1300
scans.
−1
cm .
9.4 Place the oxygen-free reference specimen (see 8.2) in
9.1.5.2 Then collect a spectrum I (v) with the sapphire wafer
s
the sample beam such that the angle of incidence is u or
iFM
(see 8.1.3) in the sample beam over the wavenumber range
−1 u as determined in 9.2.2 or 9.2.3, respectively, and collect
iSBM
from 900 to 1300 cm .
a spectrum I (v) over the wavenumber range from 900 to
FZ
9.1.5.3 Determine the ratio I (v)/I (v) over the wavenumber
0 s −1
−1 1300 cm .
range from 900 to 1300 cm .
9.5 Determines the transmittance spectrum of the oxygen-
9.1.5.4 If the ratio I (v)/I (v) # 0.001 (0.1 %) over the entire
0 s
free reference specimen as follows:
wavenumber range, the instrument is acceptable for use.
I ~v!
9.1.5.5 If the ratio I (v)/I (v) > 0.001 (0.1 %) over any part
FZ
0 s
T ~v! 5 (2)
FZ
I ~v!
of the wavenumber range, adjust the instrument in accordance 0
with the manufacturer’s instructions and repeat the entire
9.6 Remove the oxygen-free reference s
...