ASTM F84-02

Standard Test Method for Measuring Resistivity of Silicon Wafers With an In-Line Four-Point Probe (Withdrawn 2003)

SCOPE
This standard was transferred to SEMI (www.semi.org) May 2003
1.1 This test method covers the measurement of the resistivity of silicon wafers with a in-line four-point probe. The resistivity of a silicon crystal is an important materials acceptance requirement. This test method describes a procedure that will enable interlaboratory comparisons of the room temperature resistivity of silicon wafers. The precision that can be expected depends on both the resistivity of the wafer and on the homogeneity of the wafer. Round-robin tests have been conducted to establish the expected precision for measurements on  p-type wafers with room temperature (23°C) resistivity between 0.0008 and 2000 cm and on n-type wafers with room-temperature (23°C) resistivity between 0.0008 and 6000 cm.
1.2 This test method is intended for use on single crystals of silicon in the form of circular wafers with a diameter greater than 16 mm (0.625 in.) and a thickness less than 1.6 mm (0.0625 in.). Geometrical correction factors required for these measurements are available in tabulated form.
1.3 This test method is to be used as a referee method for determining the resistivity of single crystal silicon wafers in preference to Test Methods F43.
Note 1—The test method is also applicable to other semiconductor materials but neither the appropriate conditions of measurement nor the expected precision have been experimentally determined. Other geometrics for which correction factors are not available can also be measured by this test method but only comparative measurements using similar geometrical conditions should be made in such situations.
Note 2—DIN 50431 is a similar, but not equivalent, method for determining resistivity. It is equivalent to Test Methods F43.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 8.

General Information

• Status: Withdrawn
• Publication Date: 09-Dec-2002
• Withdrawal Date: 09-May-2003
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics

Standards Content (Sample)

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.
Designation: F 84 – 02
Standard Test Method for
Measuring Resistivity of Silicon Wafers With an In-Line
Four-Point Probe
This standard is issued under the fixed designation F 84; 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.
rics for which correction factors are not available can also be measured by
1. Scope
this test method but only comparative measurements using similar
1.1 This test method covers the measurement of the resis-
geometrical conditions should be made in such situations.
tivity of silicon wafers with a in-line four-point probe. The 2
NOTE 2—DIN 50431 is a similar, but not equivalent, method for
resistivity of a silicon crystal is an important materials accep-
determining resistivity. It is equivalent to Test Methods F 43.
tance requirement. This test method describes a procedure that
1.4 The values stated in SI units are to be regarded as the
will enable interlaboratory comparisons of the room tempera-
standard. The values given in parentheses are for information
ture resistivity of silicon wafers. The precision that can be
only.
expected depends on both the resistivity of the wafer and on the
1.5 This standard does not purport to address all of the
homogeneity of the wafer. Round-robin tests have been con-
safety concerns, if any, associated with its use. It is the
ducted to establish the expected precision for measurements on
responsibility of the user of this standard to establish appro-
p-type wafers with room temperature (23°C) resistivity be-
priate safety and health practices and determine the applica-
tween 0.0008 and 2000 V·cm and on n-type wafers with
bility of regulatory limitations prior to use. Specific hazard
room-temperature (23°C) resistivity between 0.0008 and 6000
statements are given in Section 8.
V·cm.
1.2 This test method is intended for use on single crystals of
2. Referenced Documents
silicon in the form of circular wafers with a diameter greater
2.1 ASTM Standards:
than 16 mm (0.625 in.) and a thickness less than 1.6 mm
D 5127 Guide for Ultra Pure Water Used in the Electronics
(0.0625 in.). Geometrical correction factors required for these
and Semiconductor Industry
measurements are available in tabulated form. 5
E 1 Specification for ASTM Thermometers
1.3 This test method is to be used as a referee method for
E 177 Practice for Use of the Terms Precision and Bias in
determining the resistivity of single crystal silicon wafers in 6
ASTM Test Methods
preference to Test Methods F 43.
F 42 Test Methods for Conductivity Type of Extrinsic
Semiconducting Materials
NOTE 1—The test method is also applicable to other semiconductor
materials but neither the appropriate conditions of measurement nor the
F 43 Test Methods for Resistivity of Semiconductor Mate-
expected precision have been experimentally determined. Other geomet-
rials
F 2074 Standard Guide for Measuring Diameter of Silicon
and Other Semiconductor Wafers
This test method is under the jurisdiction of ASTM Committee F01 on
2.2 SEMI Standard:
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon
Materials and Process Control. C19 Specification for Acetone
Current edition approved Dec. 10, 2002. Published February 2003. Originally
C28 Specifications and Guidelines for Hydrofluoric Acid
approved in 1967 as F 84 – 67 T. Last previous edition approved in 1999 as
C31 Specification for Methanol
F84–99.
C35 Specifications and Guidelines for Nitric Acid
DIN 50431 is a similar, but not equivalent, method. It is the responsibility of
DIN Committee NMP 221, with which Committee F01 maintains close liaison. DIN
50431, Testing of Inorganic Semiconductor Materials: Measurement of the Specific
Electrical Resistance of Monocrystals of Silicon or Germanium by the Four-Point
Direct-Current Technique with Linearly Arranged Probes, is available from Beuth
Verlag GmbH Burggrafenstrasse 4-10, D-1000 Berlin 30, Federal Republic of
Germany. Annual Book of ASTM Standards, Vol 11.01.
3 5
Smits, F. M., “Measurement of Sheet Resistivities with the Four-Point Probe” Annual Book of ASTM Standards, Vol 14.03.
Bell System Technical Journal, BSTJA, Vol 37, 1958, p. 711: Swartzendruber, L. J., Annual Book of ASTM Standards, Vol 14.02.
“Correction Factor Tables for Four-Point Probe Resistivity Measurements on Thin, Annual Book of ASTM Standards, Vol 10.05.
Circular Semiconductor Samples.” Technical Note 199, NBTNA, National Bureau Available from the Semiconductor Equipment and Materials International,
of Standards, April 15, 1964. 3081 Zanker Road, 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 84–02
3. Terminology many changes in these conditions may be made for nonreferee
applications without severe changes in measurement results.
3.1 Definitions of Terms Specific to This Standard:
5.3 The accuracy of the resistivity as measured by this test
3.1.1 four-point probe—an electrical probe arrangement for
method has not been determined. Systematic error is intro-
determining the resistivity of a material in which separate pairs
duced by characteristic radial nonuniformities in the resistivity
of contacts are used (1) for passing current through the
of silicon wafers and by the finite dimensions of the wafer. The
specimen and (2) measuring the potential drop caused by the
magnitude of these errors is affected by the position of the
current.
probe head on the wafer; for referee measurements the probe
3.1.2 probe head, of a four-point probe—the mounting that
head should be placed within 0.25 mm (0.01 in.) of the center
(1) fixes the positions of the four pins of the probe in a specific
of the wafer. Systematic error may also be introduced in the
pattern such as an in-line (collinear) or square array and (2)
measurement of the separation of the probe tips. The relative
contains the pin bearings and springs or other means for
error in the determination of the probe-tip spacing decreases as
applying a load to the probe pins.
the nominal probe-tip spacing increases; for referee measure-
3.1.3 probe pin, of a four-point probe—one of the four
ments a four-point probe with nominal 1.59 mm (62.5 mil)
needles supporting the probe tips; mounting in a bearing
probe-tip spacing is required.
contained in the probe head and losded by a spring or dead
5.4 The recommended analog circuit (Fig. 1) is not a perfect
weight.
model of a semiconductor wafer being contacted by four
3.1.4 probe tip, of a four-point probe—the part of the pin
metallic probes, with possible rectifying effects. The most
that contacts the wafer.
effective use of the analog circuit to test the electrical instru-
3.1.5 probe-tip spacing, of a four-point probe— the distance
mentation for possible error voltage during measurement
between adjacent probe tips.
requires that readings from opposite current polarities be
3.1.6 resistivity, r [V·cm]—of a semiconductor, the ratio of
treated separately, and not averaged. In this manner, the
the potential gradient (electric field) parallel with the current to
calculated standard deviation of the analog measurements will
the current density.
have enhanced sensitivity to possible error voltages.
6. Interferences
4. Summary of Test Method
6.1 In making resistivity measurements, spurious results can
4.1 An in-line four-point probe is used in determining the
arise from a number of sources.
resistivity in this test method. A direct current is passed through
6.1.1 Photoconductive and photovoltaic effects can seri-
the specimen between the outer probe pins and the resulting
ously influence the observed resistivity, particularly with
potential difference is measured between the inner probes. The
nearly intrinsic material. Therefore, all determinations should
resistivity is calculated from the measured current and potential
be made in a dark chamber unless experience shows that the
values using factors appropriate to the geometry.
material is insensitive to ambient illumination.
4.2 This test method includes procedures for checking both
6.1.2 Spurious currents can be introduced in the testing
the probe head and the electrical measuring apparatus.
circuit when the equipment is located near high frequency
4.2.1 The spacing between the four probe tips is determined
generators. If equipment is located near such sources, adequate
from measurements of indentations made by the probe tips in
shielding must be provided.
a polished silicon surface. This test also is used to determine
6.1.3 Minority carrier injection during the measurement can
the condition of the probe tips.
occur due to the electric field in the specimen. With material
4.2.2 The accuracy of the electrical measuring equipment is
possessing high lifetime of the minority carriers and high
tested by means of an analog circuit containing a known
standard resistor together with other resistors which simulate
the resistance at the contacts between the probe tips and the
Ehrstein, J. R.; Brewer, F. H.; Ricks, D. R.; and Bullis, W. M., “Effects of
semiconductor surface.
Current, Probe Force, and Wafer Surface Condition on Measurement of Resistivity
4.3 Procedures for preparing the specimen, for measuring
of Bulk Silicon Wafers by the Four-Probe Method,” Appendix E, “Methods of
its size, and for determining the temperature of the specimen Measurement for Semiconductor Materials, Process Control, and Devices,” Tech-
nical Note 773 , NBTNA, National Bureau of Standards, June 1973, pp. 43–49.
during the measurements are also given. Abbreviated tables of
Available as COM 73-50534 from National Technical Information Service, Spring-
correction factors appropriate to circular wafer geometry and a
field, VA 22161.
table of temperature coefficient versus resistivity are included
with the test method so that appropriate calculations can be
made conveniently.
5. Significance and Use
5.1 Resistivity values measured by this test method are a
primary quantity for characterization and specification of
silicon material used for semiconductor electronic devices.
5.2 The current level, probe force, and specimen surface
preparation specified in this test method are to be preferred for
NOTE 1—See Table 2 for appropriate values of r.
all referee measurements on bulk silicon wafers. However, FIG. 1 Analog Test Circuit to Simulate Four-Probe Measurement
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 84–02
resistivity, such injection can result in a lowering of the 7. Apparatus
resistivity for a distance of several centimetres. Carrier injec-
7.1 Slice Preparation:
tion can be detected by repeating the measurements at lower
7.1.1 Lapping Facilities which permit the lapping of a
current. In the absence of injection no increase in resistivity
wafer so that the thickness varies by no more than 61 % from
should be observed. For specimens thicker than 0.75 mm
its value at the center.
(0.030 in.) use of the currents recommended in Table 1 should
7.1.2 An Ultrasonic Cleaner of suitable frequency (18 to 45
reduce the probability of difficulty from this source to a
kHz) and adequate power.
minimum. In cases of doubt and for thinner specimens the
7.1.3 Chemical Laboratory Apparatus such as plastic bea-
measurements of 12.4 and 12.5 should be repeated at a lower
kers, graduates, and plastic-coated tweezers suitable for use
current. If the proper current is being used, doubling or halving
both with acids (including hydrofluoric) and with solvents.
its magnitude should cause a change in observed resistance
Adequate facilities for handling and disposing of acids and
which is less than 0.5 %.
their vapors are essential.
6.1.4 Semiconductors have a significant temperature coeffi-
7.2 Measurement of Specimen Geometry:
cient of resistivity. Consequently, the current used should be
7.2.1 Thickness—Calibrated mechanical or electronic thick-
small to avoid resistive heating. If resistive heating is suspected
ness gage capable of measuring the wafer thickness to 61.0 %
it can be detected by a change in readings as a function of time
(R3S%) at various positions on the wafer.
starting immediately after the current is applied.
7.2.2 Diameter—A micrometer or vernier caliper.
6.1.5 Vibration of the probe sometimes causes troublesome
7.3 Probe Assembly:
changes in contact resistance. If difficulty is encountered, the
7.3.1 Probe Pins with conical tungsten carbide probe tips
apparatus should be shock mounted.
with included angle of 45 to 150°. The nominal radius of a
6.1.6 The temperature corrections given in this test method
probe tip should be initially 25 to 50 μm.
are valid only if the temperature of the specimen during
7.3.2 Probe Force— The force on each probe shall be 1.75
measurement is held constant in the range from 18 through
6 0.25 N when the probe pins are against the specimen in
28°C.
measurement position.
6.1.7 It is not uncommon with modern digital voltmeters to
7.3.3 Insulation—For measurement of specimens with re-
find that the voltmeter itself provides a source of current of the
sistivity up to approximately 100 V·cm, the electrical isolation
order of 10 pA between its high and low input terminals.
between a probe pin (with its associated spring and external
Currents of this magnitude will generally have no effect on
lead) and any other probe pin or part of the probe head shall be
measurement accuracy for specimens below about 1000 V·cm.
at least 100 MV. For measurement of specimens with higher
However, since such spurious currents flow through the contact
resistivity, the electrical isolation in ohms should be at least a
resistance of the voltage sensing probes, which contact resis-
factor of 1 M times the specimen resistivity in ohm centimetre.
tances may be many megohms for higher resistivity specimens,
7.3.4 Probe Alignment and Separation—The four probe tips
the result may be spurious voltages of several tens of micro-
shall be in an equally spaced linear array. The probe-tip spacing
volts. These spurious currents can often be reduced if the
shall have a nominal value of 1.59 mm (62.5 mils). Probe–tip
autozero and auto calibration functions of the voltmeter can be
spacing shall be determined in acco
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