ASTM F1619-95(2000)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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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.
1. Scope surface of the wafer is mirror polished and the back surface
may be as-cut, lapped, or etched (see 8.1.1.1).
1.1 This test method covers determination of the absorp-
1.4 This test method is applicable to silicon wafers with
tion coefficient due to the interstitial oxygen content of
resistivity greater than 5 V·cm at room temperature.
commercial monocrystalline silicon wafers by means of Fou-
1.5 This standard does not purport to address all of the
rier transform infrared (FT-IR) spectroscopy. In this test
safety concerns, if any, associated with its use. It is the
method, the incident radiation is p-polarized and incident on
responsibility of the user of this standard to establish appro-
the test specimen at the Brewster angle in order to minimize
3 priate safety and health practices and determine the applica-
multiple reflections.
bility of regulatory limitations prior to use.
NOTE 1—In this test method, radiation in which the electric vector is
parallel to the plane of incidence is defined as p-polarized radiation.
2. Referenced Documents
NOTE 2—Committee F-1 has been advised that some aspects of this test
2.1 ASTM Standards:
method may be subject to a patent applied for by Toshiba Ceramics
4 F 1188 Test Method for Interstitial Atomic Oxygen Content
Corporation. The Committee takes no position with respect to the
of Silicon by Infrared Absorption
applicability or validity of such patents, but it requests users of this test
method and other interested parties to supply any information available on F 1241 Terminology of Silicon Technology
non-patented alternatives for use in connection with this test method.
2.2 SEMI Standard:
SEMI M1 Specifications for Polished Monocrystalline
1.2 Since the interstitial oxygen concentration is propor-
−1
Silicon Wafers
tional to the absorption coefficient of the 1107 cm absorption
band, the interstitial oxygen content of the wafer can be
3. Terminology
derived directly using an independently determined calibration
3.1 Definitions of terms related to silicon technology are
factor.
found in Terminology F 1241.
1.3 The test specimen is a single-side polished silicon wafer
3.2 Definitions of terms related specifically to FT-IR spec-
of the type specified in SEMI Specifications M1. The front
troscopy are found in Test Method F 1188.
4. Summary of Test Method
This test method is under the jurisdiction of ASTM Committee F01 on
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon 4.1 The stability of the FT-IR spectrometer is established to
Materials and Process Control.
be adequate for the measurement cycle.
Current edition approved Sept. 15, 1995. Published November 1995.
4.2 The optimum angle of incidence is determined to
This standard is based on draft procedures and interlaboratory tests conducted
minimize multiple internal reflection.
by the Silicon Wafer Committee of the SEMI Japan Standards Program and the
Oxygen and Carbon Measurement Committee of the Japan Electronic Industry
4.3 The transmission spectrum of an oxygen-free double-
Development Association (JEIDA).
side polished float-zone wafer is recorded.
Krishnan, K., “Precise and Rapid Measurement of Oxygen and Carbon in
4.4 The transmission spectrum of the oxygen-containing
Silicon,” Defects in Silicon, edited by W. M. Bullis and L. C. Kimerling,
test specimen is determined.
Proceedings Volume 83-9, The Electrochemical Society, Pennington, NJ, 1983, pp.
285–292; Shirai, H., “Determination of Oxygen Concentration in Single-Side
4.5 The negative logarithm of each of these transmission
Polished Czochralski-Grown Silicon Wavers by p-Polarized Brewster Angle Inci-
spectra is taken to determine the absorbance spectra.
dence Infrared Spectroscopy,” Journal of The Electrochemical Society, Vol 138, No.
4.6 The absorbance spectra are normalized by dividing by
6, 1991, pp. 1784–1787; Shirai, H., “Oxygen Measurements in Acid-Etched
Czochralski-Grown Silicon Wafers,” Journal of The Electrochemical Society,Vol
the beam path length to obtain the absorption coefficient as a
139, No. 11, 1992, pp. 3272–3275.
function of wavenumber.
“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, 805 E.
8627. Middlefield Rd., Mountain View, CA 94043.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F 1619
4.7 The baseline is corrected for curvature resulting from 5°C during the measurement as required by Test Method
scattering from the rough back surface and the baseline value F 1188.
−1
at 1107 cm is determined. 6.7 Nonlinearity in the spectrometer and its detecting
4.8 This baseline value is subtracted from the absorbance at system can degrade the accuracy of the measurement.
−1
1107 cm to determine the absorption coefficient due to
7. Apparatus
interstitial oxygen.
7.1 Single-Beam Fourier Transform Infrared Spectrometer,
4.9 The absorption coefficient is multiplied by the appropri-
as specified in Test Method F 1188, capable of collecting
ate calibration factor to obtain the oxygen content of the test
−1
transmission spectra with resolution of both 4 cm and 1
specimen.
−1
cm .
7.2 Polarizer, in order that the incident beam shall be
5. Significance and Use
p-polarized.
5.1 Control of the oxygen content is essential for silicon
7.3 The central angle of the incident beam flux shall be
wafers to be used for advanced devices and integrated circuits.
adjustable between 65° and 75° from the surface normal.
It is desirable to be able to measure the oxygen content of
7.4 Detector shall be large enough that the shifting of the
product wafers, nondestructively and without regard for back
beam by the sample (a lateral distance equal to 0.88 times the
surface finish. This test method provides a means for reducing
sample thickness) does not affect its sensitivity. Detector
the influence of the back surface condition on the measure-
sensitivity shall be unchanged whether a sample is or is not in
ment.
the measurement beam.
5.2 This test method may be used for routine process
monitoring, quality control, materials acceptance, and research
8. Test and Reference Specimens
and development.
8.1 Test Specimen:
8.1.1 A silicon wafer with chem-mechanically polished
6. Interferences
front surface and a back surface that may be as-cut, lapped or
6.1 Multiple Reflections are greatest for thin, double-side
etched. The back-surface roughness shall be such that:
polished wafers with parallel front and back surfaces. In this
8.1.1.1 The rms roughness shall be less than 0.9 μm,
−1
case, the transmittance, T, is given as follows:
8.1.1.2 The transmittance through the wafer at 1107 cm
2 2ax
shall equal or exceed 25 %, or
~1 2 R! e
2 2ax 2 22ax 4 24ax
T 5 5 ~1 2 R! e @1 1 R e 1 R e 1 .#
2 22ax 8.1.1.3 The difference between the absorption coefficient at
1 2 R e
−1 −1
1200 cm and the absorption coefficient at 950 cm shall be
(1)
−1
positive but less than 5 cm .
where:
8.1.2 Wafers shall have thickness in the range specified in
R = reflectance ratio,
SEMI Specifications M1 (between 500 and 750 μm for wafers
−1
a = absorption coefficient in cm , and
with diameter from 100 to 200 mm). Measure and record as
x = optical path length in cm ( = d/cos u , where
r
d the thickness of each test specimen to the nearest μm.
CZ
d = specimen thickness, in cm, and u = angle of
r
8.1.3 The resistivity of either n-or p-type test specimens
refraction (see 10.1).
shall be greater than 5 V·cm.
2 −2ax
To neglect multiple reflections, the quantity R e should
8.2 Oxygen-Free Reference Specimen:
be less than 0.001. The reflection is suppressed for incident
8.2.1 A double-side polished, float-zoned silicon wafer with
radiation at the Brewster angle (73.7° from the normal in 16 3
maximum oxygen content of 1 3 10 atoms/cm (0.2 ppma)
silicon). However, because of the large cone angle of the
and resistivity greater than 5 V·cm.
incident radiation in FT-IR spectrometers with focused beam
8.2.2 Measure and record as d the thickness to the nearest
FZ
not all of the radiation is precisely at the Brewster angle.
μm; the thickness of the reference specimen shall be within
Procedures to minimize this effect are given in 9.2.
620 % of that of the test specimen.
6.2 Optical Path Length of the transmitted beam is esti-
8.3 A second double-side polished, float-zoned wafer, ;400
mated from the central beam angle of the incident non-parallel
μm thick, for use in determining the optimum angle of
beam flux.
incidence.
6.3 Surface Scattering—the baseline that is due largely to
8.4 Sapphire wafer $400 μm-thick, polished on one or both
surface scattering is approximated by a parabolic curve (see
sides.
Appendix X1).
9. Procedure
6.4 Free Carrier Absorption is minimized by requiring that
the resistivity of the test and reference specimens be greater
9.1 Determine Stability of FT-IR Spectrometer:
than 5 V·cm.
9.1.1 Turn on the spectrometer and allow it to operate long
6.5 Reference Wafer is required in order to determine the
enough to stabilize.
−1
absorption due to the silicon lattice spectrum at the wavenum- 9.1.2 Set the resolution of the spectrometer to 4 cm .
ber of the peak of the oxygen absorption.
9.1.3 Use a minimum of 64 scans for each spectrum
6.6 Temperature Control—Since both oxygen and silicon collection.
lattice absorption change with temperature, the temperature 9.1.4 100 % Line Check:
inside the spectrometer chamber must be maintained at 27 6 9.1.4.1 Collect a background spectrum I (v) with the
F 1619
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- cm with the thin, double-side polished, float-zoned wafer
01 02
−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 (100.06 9.2.3.3 Rotate the specimen holder so that angle of inci-
01 02
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 increase as the angle of incidence approaches the Brewster
01 02
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
−1
until the ratio I ( v)/I (v) = 1.000 6 0.005 over the entire each time until the transmitted intensity at 1107 cm begins
01 02
wavenumber range. to 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
−1
using a single background spectrum is completed within the
the maximum transmitted intensity at 1107 cm as u .
isBM
time interval t minutes. 9.3 Collect a background spectrum I over the wavenumber
−1
9.1.5 0 % Line Check:
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 the sample beam such that the angle of incidence is u or
s iFM
wafer (see 8.1.3) in the sample beam over the wavenumber u as determined in 9.2.2 or 9.2.3, respectively, and collect
isBM
−1
range from 900 to 1300 cm .
a spectrum I (v) over the wavenumber range from 900 to
FZ
−1
9.1.5.3 Determine the ratio I (v)/I (v) over the wavenumber 1300 cm .
0 s
−1
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 free reference specimen as follows:
0 s
entire wavenumber range, the instrument is acceptable for use.
I ~v!
FZ
T ~v! 5 (2)
9.1.5.5 If the ratio I (v)/I ( v) > 0.001 (0.1 %) over any part FZ
0 s
I ~v!
of the wavenumber range, adjust the instrument in accordance
9.6 Remove the oxygen-free reference specimen.
with the manufacturer’s instructions and repeat the entire
9.7 Place a test specimen (see 8.1) in the sample beam so
procedure beginning with 9.1.
that the angle of incidence is u and collect a spectrum I (v)
i CZ
9.2 Angle of Incidence:
−1
over the wavenumber range from 900 to 1300 cm .
9.2.1 Use one of the following two methods to determine
9.8 Determine the transmittance spectrum of the test speci-
the best angle of incidence of the p-polarized infrared beam.
men as follows:
9.2.2 Fringe Minimum (FM) Method:
−1
I ~v!
9.2.2.1 Set the resolution of the spectrometer to 1 cm .
CZ
T ~v! 5 (3)
CZ
I ~v!
9.2.2.2 Adjust the angle of the specimen holder so that the 0
angle of incidence to a value somewhat larger than the
9.9 If desired, determine the transmittance spectra of addi-
Brewster angle, and collect a spectrum I ( v) with the thin
t
...