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SEMI MF671-0705 © SEMI 2003, 2005 6 or not the wafer was edge round ed. For this situation, the sample standard deviation is a valid measu re of the measurement variability. 13.4.1 The two-sigm a standard deviation for a…
SEMI MF671-0705 © SEMI 2003, 2005 5
10.7 To determine the location of the end of the flatted
region, use the point at which the wafer image on the
comparator screen is one division away from the horizontal
reference line. This corresponds to an offset of 50 m
(0.002 in.) on the wafer. (See Figure 5.)
10.8 Record the micrometer reading to the nearest 25 m or
0.001 in. as E
l
(left) on the data sheet (see example in
Figure 6).
10.9 Scan the projected image of the flat using the x-axis
micrometer so that the right end is coincident with the
intersection of the vertical and horizontal reference lines.
10.10 Determine the location of the right end of the flatted
region using the offset procedure described in ¶10.7.
10.11 Record the micrometer reading to the nearest 25 m
or 0.001 in. as E
r
(right) on the data sheet.
11 Calculation
11.1 Compute flat length, l, for each sample as follows:
rl
EEl (1)
11.2 Record the values obtained on the data sheet.
12 Report
12.1 Report the following information:
12.1.1 Date of test,
12.1.2 Operator and laboratory identification,
12.1.3 Comparator make and model, together with nominal viewing screen diameter,
12.1.4 Wafer identification,
12.1.5 Wafer nominal diameter, and
12.1.6 Measured flat length.
13 Precision
4
13.1 An interlaboratory evaluation of this test method was conducted in which seven laboratories made
measurements on 18 silicon wafers, 10 of which were edge rounded by mechanical grinding. Wafers with nominal
diameters of 2 in., 3 in., 100 mm, and 125 mm were included. Each wafer contained a secondary flat in one of the
secondary flat configurations specified in SEMI M1. The nominal flat lengths ranged from 6 mm (0.2 in.) to 40 mm
(1.6 in.).
13.2 Each participating laboratory was requested to report three replicate sets of data. However, only 17 data sets
were reported. Therefore, the within-laboratory repeatability could not be reliably estimated.
13.3 The offset requirement of ¶10.7 which was specified as 100 m (0.004 in.) at the time of the test was not
applied consistently; its efficacy cannot be verified from the reported results.
13.4 Because of the foregoing limitations, all the reported data were pooled to estimate the between-laboratory
reproducibility. The variabilities of measured flat length were independent of both the nominal length and whether
4 Supporting data are available on request from SEMI Headquarters, 3081 Zanker Road, San Jose, CA, Telephone 408-943-7021, Fax: 408-943-
7015, e-mail: standards@semi.org. Request International Standards Research Report 1002.
N
OTE: This figure illustrates the use of offset with
a two division offset, but the procedure of the text
method requires use of a one division offset
Figure 5
Illustration of the Use of Offset
SEMI MF671-0705 © SEMI 2003, 2005 6
or not the wafer was edge rounded. For this situation, the sample standard deviation is a valid measure of the
measurement variability.
13.4.1 The two-sigma standard deviation for all wafers was ±1.5 mm (0.060 in.) or less.
13.4.2 For 90% of all wafers, the two-sigma standard deviation was ±1.2 mm 0.046 in.) or less.
FLAT LENGTH DETERMINATION
Laboratory __________________
Test Operator __________________
Comparator Make and Model __________________
Viewing Screen Diameter __________
Date of
Test
Wafer
Identi-
fication
Nominal
Wafer
Diameter
E
l
E
r
Flat
Length
(E
l
E
r
)
Figure 6
Suggested Data Sheet Format
14 Keywords
14.1 flat; optical comparator; primary flat; secondary flat; semiconductor; silicon; wafer
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SEMI MF674-0705 © SEMI 2003, 2005 1
SEMI MF674-0705
PRACTICES FOR PREPARING SILICON FOR SPREADING
RESISTANCE MEASUREMENTS
These practices were technically approved by the global Silicon Wafer Committee. This edition was approved for
publication by the global Audits and Reviews Subcommittee on April 7, 2005. It was available at www.semi.org in
June 2005 and on CD-ROM in July 2005. Original edition published by ASTM International as ASTM F 674-80. Last
previous edition SEMI MF674-92 (Reapproved 1999).
1 Purpose
1.1 Resistivity is probably the single most important parameter for the characterization of silicon starting material
for semiconductor device fabrication. Spreading resistance measurements are used to measure resistivity variations
in raw silicon crystals and completed semiconductor devices. The reproducibility of spreading resistance
measurements on silicon specimens is known to depend on the manner of specimen preparation. The interpretation
of spreading resistance measurements depends in turn on the reproducibility of test specimen measurements and on
the reproducibility of calibration specimen measurements.
1.2 The procedures given are intended to confer a high degree of reproducibility to spreading resistance
measurements, and offer improvement over other preparation techniques.
1
2 Scope
2.1 These practices cover the surface preparation of silicon samples using diamond polishing prior to measurement
of resistivity variations by the spreading resistance technique.
NOTE 1: Benefits derived from diamond polishing are (1) stability and reproducibility of spreading resistance values on large
area or beveled specimens, and (2) acuity of beveled surface geometry. The benefits of stability and reproducibility are likely to
apply to both conductivity types and all resistivity values; however, they have been demonstrated extensively only for (111) n-
type above 1 ·cm. Enhanced bevel acuity is independent of conductivity-type or resistivity value.
2.2 Separate practices are given for preparation of large-area specimens for measurement of lateral resistivity
variations and for preparation of bevel-sectioned specimens (usually small chips) for measurement of vertical
variations of resistivity (depth profiling).
2.3 The two practices are covered as follows:
Front-Surface Diamond Polishing §7 through §9
Diamond Bevel Polishing §10 through §12
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 Polishing of silicon with diamond causes light but controllable and uniform scratch damage to the silicon
surface. Nevertheless, such uniform damage is compatible with spreading resistance measurement data having very
low scatter. Contamination of the polishing medium with hard foreign particles can cause random heavy scratch
damage to a specimen. If encountered by the spreading resistance probes, heavily scratch-damaged regions may
yield erratic measurement results.
3.2 Contamination of the specimen with water subsequent to polishing may adversely affect the reproducibility of
spreading resistance measurements.
1 Ehrstein, J. R., Ricks, D. R. and Robinson, L. A., “Spreading Resistance Measurements, Measurement Techniques for High Power
Semiconductor Materials and Devices,” Annual Report, Oct. 1, 1977 to Sept. 30, 1978, NBSIR 79-1756, F.F. Oettinger, ed.