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SEMI MF1618-1104 © SEMI 2004 10 NOTICE: SEMI makes no warranties or representations as to the suitability of the standards set forth herein for any particular application. The determination of the suitability o f the sta…

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SEMI MF1618-1104 © SEMI 2004 9
Table A1-2 Approximate Number of Measurement
Sites for Various Numbers of Rows and Columns in
a Cartesian Sampling Plan
Number of
rows and
columns
7 9 11 13 15 17
Number of
sites
37 69 97 137 177 225
A1-4.3 The size of the cells, and the separation of the
measurement sites along the x- and y-axes, is
determined by the number of rows and columns into
which the wafer surface is partitioned. Use Table A1-2
as a guide to the approximate number of measurement
sites for various numbers of rows and columns of cells.
To calculate the dimensions of the square cells, divide
the outermost radius, R
o
, determined in Section A1.1,
by N, the desired number of rows and columns. The
exact number of sites that will be measured is governed
by the number of cells near the wafer perimeter that
need to be excluded because the center of the cell, that
is, the center of the measurement spot, does not fall
within the radius R
o
.
A1-4.4 Use test instrument software to establish the
coordinates of the center of all cells as determined from
the ratio R
o
/N
C
, calculated in Section A1-4.3. Disallow
measurement sites near the wafer perimeter such that
the radial distance to the center of the cell, that is, the
center of the measurement spot, is larger than R
o
. This
follows the same rationale for allowed measurement
sites as is used with the concentric circle plans.
A1-4.5
Take measurements at all sites allowed in
accordance with Table A1-2. The measurement
sequence, whether starting from the center point and
moving outward or starting from one edge a row or
column at a time, is to be decided by the parties to the
test.
A1-4.6
Calculate the uniformity based on the difference
between the maximum and minimum measured values,
HLV(%), and on the standard deviation as a percent of
the mean of all measurements, SUP(%), as detailed in
Section 9.3.
A1-5 Single-Diameter Sampling Plan
A1-5.1 This plan uses a very high density of
measurements along a diameter and includes a
measurement at the wafer center. It is shown
schematically in Figure A1-4 for the diameter being
parallel to a major wafer flat. However, in the case of
notched wafers, the notch would replace the flat in the
figure. It is also possible, by agreement of the parties to
the test, to make the measurements along a diameter at
a specified angle with respect to the fiducial axis as
long as such an angle is then stated in the report.
A1-5.2
Choose a value, N
M
, for the number of
measurements, where N
M
is at least 25. The separation
between measurement sites is given by 2R
o
/(N
M
1),
where R
o
is determined as in Section A1-1.1.
2R
o
/(N
M
–1)
NOTE: The radius R
o
is given by Equation A1-1 for Method
A and by Equation A1-2 for Method B.
Figure A1-4
Illustration of Single-Diameter, High-Density
Measurement Site Plan
A1-5.2.2 Compare the site separation, 2R
o
/(N
M
1),
with the estimated measurement sampling area or spot
size. If the interval is smaller than this value, little
additional information may be obtained by choosing so
large a value for N
M
; it may be appropriate to reduce N
M
so that the new calculated site separation is equal to or
greater than the measurement sampling area.
A1-5.3
Establish the coordinates for all measurement
sites using the site interval value just calculated and the
wafer center as the reference point. Take
measurements at all sites.
A1-5.4
Calculate the uniformity based on the difference
between the maximum and minimum measured values,
HLV(%), and on the standard deviation as a percent of
the mean of all measurements, SUP(%), as detailed in
Section 9.3.
SEMI MF1618-1104 © SEMI 2004 10
NOTICE: SEMI makes no warranties or
representations as to the suitability of the standards set
forth herein for any particular application. The
determination of the suitability of the standard is solely
the responsibility of the user. Users are cautioned to
refer to manufacturer’s instructions, product labels,
product data sheets, and other relevant literature,
respecting any materials or equipment mentioned
herein. These standards are subject to change without
notice.
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Equipment and Materials International (SEMI) takes no
position respecting the validity of any patent rights or
copyrights asserted in connection with any items
mentioned in this standard. Users of this standard are
expressly advised that determination of any such patent
rights or copyrights, and the risk of infringement of
such rights are entirely their own responsibility.
Copyright by SEMI® (Semiconductor Equipment and Materials
International), 3081 Zanker Road, San Jose, CA 95134. Reproduction
of the contents in whole or in part is forbidden without express
written consent of SEMI.
SEMI MF1630-0704 © SEMI 2004 1
SEMI MF1630-0704
TEST METHOD FOR LOW TEMPERATURE FT-IR ANALYSIS OF
SINGLE CRYSTAL SILICON FOR III-V IMPURITIES
This test method was technically approved by the Global Silicon Wafer Committee and is the direct
responsibility of the North American Silicon Wafer Committee. Current edition approved for publication by
the North American Regional Standards Committee on March 14, 2004. Initially available at
www.semi.org
May 2004; to be published July 2004. Original edition published by ASTM International as ASTM F 1630-
95. Last previous edition SEMI MF1630-00.
1 Purpose
1.1 Electronic grade polysilicon producers and users
rely on LTFT-IR spectroscopy to evaluate polysilicon
for quality assurance and research purposes.
1.2 LTFT-IR spectroscopy identifies and quantitates
boron, phosphorus, aluminum, arsenic, indium,
antimony, and gallium.
1.3 LTFT-IR spectroscopy can be applied to FZ, CZ, or
other single crystal silicon (either doped or undoped) up
to the concentration limits given in Section 2.2.
1.4 The measurement of carbon in silicon at low
temperature can be accomplished concurrently in
accordance with SEMI MF1391. The carbon can be
measured at lower concentrations at <15 K than is
possible at room temperature because the two-phonon
band transmission is increased by a factor of two
allowing greater throughput to the detector that results
in an increased signal to noise ratio. Also the carbon
adsorption band narrows from a FWHM of 5 to 6 cm
−1
to a FWHM of 2.5 to 3.0 cm
−1
at these low
temperatures.
2 Scope
2.1 This test method covers the determination of
electrically active boron, phosphorus, arsenic,
aluminum, antimony, and gallium concentration in
single crystal silicon.
2.2 This test method can be used for silicon in which
the impurity/dopant concentrations are between 0.01
ppba and 5.0 ppba for each of the electrically active
elements.
2.3 The concentration for each impurity/dopant can be
obtained by application of Beer’s Law. Calibration
factors are given for each element.
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.
3 Limitations
3.1 The sample specimen must be colder than 15 K for
measurement of electrically active species. If the
sample specimen is mounted on a cold finger, care must
be taken to obtain good contact between the sample
specimen and the cold finger for efficient heat transfer.
The oxygen absorption lines at 1136 cm
−1
and 1128
cm
−1
are sensitive to temperature and can be used to
determine the specimen temperature.
1
When the
sample specimen is less than 15 K the net absorbance at
1136 cm
−1
is three times larger than the net absorbance
at 1128 cm
−1
. A ratio of greater than three is obtained
for temperatures below 15 K.
3.2 Without sufficient incident white light the
compensated donors and acceptors will not absorb.
Therefore, the white light intensity must be great
enough to completely neutralize all the compensated
donors and acceptors. The intensity of the white light
necessary must be determined for each system. The
user should increase the intensity of the white light until
further increase in intensity no longer affects the
area/height of the electrically active impurity/dopant
peaks.
3.3 Water vapor absorption interferes with the
measurement of several peaks. Consequently, the
background spectrum should be collected at least daily.
The entire light path, including the sample chamber,
must be purged to remove moisture. Special care
should be taken whenever a sample specimen is
changed so that the moisture level in the sample
chamber or elsewhere in the light path is not affected.
3.4 Oxygen level in Czochralski silicon can be high
enough to exhibit thermal donor absorption lines.
These lines fall between 400 cm
−1
and 550 cm
−1
and
can interfere with aluminum (473 cm
−1
), gallium (548
cm
−1
), and occasionally arsenic (382 cm
−1
). Thermal
donors can be removed by annealing the sample
specimen.
1 Rome, J. J., “Calibration Relationships for Optically Measuring the
Concentrations of Boron, Gallium and Indium in Silicon,” Thesis,
School of Engineering, Air Force Institute of Technology (1982), pp.
46–47.