ASTM F673-90(1996)e1
(Test Method)Standard Test Methods for Measuring Resistivity of Semiconductor Slices or Sheet Resistance of Semiconductor Films with a Noncontact Eddy-Current Gage
Standard Test Methods for Measuring Resistivity of Semiconductor Slices or Sheet Resistance of Semiconductor Films with a Noncontact Eddy-Current Gage
SCOPE
1.1 These test methods cover the nondestructive measurement of bulk resistivity of silicon and certain gallium-arsenide slices and of the sheet resistance of thin films of silicon or gallium-arsenide fabricated on a limited range of substrates at the slice center point using a noncontact eddy-current gage.
1.1.1 The measurements are made at room temperature between 18 and 28°C.
1.2 These test methods are presently limited to single-crystal and polycrystalline silicon and extrinsically conducting gallium-arsenide bulk specimens or to thin films of silicon or gallium-arsenide fabricated on relatively high resistivity substrates but in principle can be extended to cover other semiconductor materials.
1.2.1 The bulk silicon or gallium-arsenide specimens may be single crystal or poly crystal and of either conductivity type (p or n) in the form of slices (round or other shape) that are free of diffusions or other conducting layers that are fabricated thereon, that are free of cracks, voids or other structural discontinuities, and that have (1) an edge-to-edge dimension, measured through the slice centerpoint, not less than 25 mm (1.00 in.); (2) thickness in the range 0.1 to 1.0 mm (0.004 to 0.030 in.), inclusive, and (3) resistivity in the range 0.001 to 200 [omega][dot]cm, inclusive. Not all combinations of thickness and resistivity may be measurable. The instrument will fundamentally be limited to a fixed sheet resistance range such as given in 1.2.2; see also 9.3.
1.2.2 The thin films of silicon or gallium-arsenide may be fabricated by diffusion, epitaxial or ion implant processes. The sheet resistance of the layer should be in the nominal range from 2 to 3000 [omega] per square. The substrate on which the thin film is fabricated should have a minimum edge to edge dimension of 25 mm, measured through the centerpoint and an effective sheet resistance at least 1000 X that of the thin film. The effective sheet resistance of a bulk substrate is its bulk resistivity (in [omega][dot]cm) divided by its thickness in cm.
1.2.3 Measurements are not affected by specimen surface finish.
1.3 These test methods require the use of resistivity standards to calibrate the apparatus (see 7.1), and a set of reference specimens for qualifying the apparatus (see 7.2).
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.
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Designation: F 673 – 90 (Reapproved 1996)
Standard Test Methods for
Measuring Resistivity of Semiconductor Slices or Sheet
Resistance of Semiconductor Films with a Noncontact
Eddy-Current Gage
This standard is issued under the fixed designation F 673; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Keywords were added editorially in January 1996.
INTRODUCTION
This test method is intended to outline the principles of eddy-current measurements as they relate
tosemiconductorsubstratesandcertainthinfilmsfabricatedonsuchsubstratesaswellasrequirements
for setting up and calibrating such instruments for use particularly at a buyer-seller interface. Because
such eddy-current measurements for semiconductor materials are made almost exclusively with
commercialinstrumentationfromoneofseveralsuppliers,somedetailsincludedheresuchasspecific
range limits and manner of entering slice/wafer thickness values to obtain resistivity values may not
apply strictly to all instruments. In all such cases, the owner’s manual for the particular instrument
shall be considered to contain the correct information for that instrument. It is to be noted that an
eddy-current instrument directly measures conductance of a specimen. Values of sheet resistance and
resistivity are calculated from the measured conductance, with the resistivity values also requiring a
measurement of specimen thickness.
1. Scope thereon, that are free of cracks, voids or other structural
discontinuities, and that have (1) an edge-to-edge dimension,
1.1 These test methods cover the nondestructive measure-
measured through the slice centerpoint, not less than 25 mm
ment of bulk resistivity of silicon and certain gallium-arsenide
(1.00 in.); (2) thickness in the range 0.1 to 1.0 mm (0.004 to
slices and of the sheet resistance of thin films of silicon or
0.030 in.), inclusive, and ( 3) resistivity in the range 0.001 to
gallium-arsenide fabricated on a limited range of substrates at
200 V·cm, inclusive. Not all combinations of thickness and
the slice center point using a noncontact eddy-current gage.
resistivity may be measurable. The instrument will fundamen-
1.1.1 The measurements are made at room temperature
tally be limited to a fixed sheet resistance range such as given
between 18 and 28°C.
in 1.2.2; see also 9.3.
1.2 These test methods are presently limited to single-
1.2.2 The thin films of silicon or gallium-arsenide may be
crystal and polycrystalline silicon and extrinsically conducting
fabricated by diffusion, epitaxial or ion implant processes.The
gallium-arsenide bulk specimens or to thin films of silicon or
sheet resistance of the layer should be in the nominal range
gallium-arsenide fabricated on relatively high resistivity sub-
from 2 to 3000 V per square. The substrate on which the thin
strates but in principle can be extended to cover other semi-
film is fabricated should have a minimum edge to edge
conductor materials.
dimension of 25 mm, measured through the centerpoint and an
1.2.1 The bulk silicon or gallium-arsenide specimens may
effective sheet resistance at least 1000 3that of the thin film.
be single crystal or poly crystal and of either conductivity type
The effective sheet resistance of a bulk substrate is its bulk
(por n)intheformofslices(roundorothershape)thatarefree
resistivity (in V·cm) divided by its thickness in cm.
of diffusions or other conducting layers that are fabricated
1.2.3 Measurements are not affected by specimen surface
finish.
This test method is under the jurisdiction of ASTM Committee F01 on
1.3 These test methods require the use of resistivity stan-
Electronics and is the direct responsibility of Subcommittee F01.06 on Electrical
dardstocalibratetheapparatus(see7.1),andasetofreference
and Optical Measurement.
specimens for qualifying the apparatus (see 7.1.2).
Current edition approved April 27, 1990. Published June 1990. Originally
published as F673–80. Last previous edition F673–89.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Please
contact ASTM International (www.astm.org) for the latest information.
´1
F 673 – 90 (1996)
1.4 The values stated in SI units are to be regarded as the 3.2.3 For subsequent measurement of thin film specimens,
standard. The values given in parentheses are for information the sheet conductance is measured, converted to sheet resis-
only. tance, and displayed. See 9.1.3 for relations between these
1.5 This standard does not purport to address all of the quantitites.
safety concerns, if any, associated with its use. It is the 3.3 MethodIIassumesinstrumentlinearitybetweencalibra-
responsibility of the user of this standard to establish appro- tion standards whose values are narrowly separated (typically
priate safety and health practices and determine the applica- 625% of the anticipated sample range median point).
bility of regulatory limitations prior to use. 3.3.1 The apparatus is first calibrated using standards of
known resistivity or sheet resistance. The apparatus is then
2. Referenced Documents
subjectedtoatestthatquantifiesapparatusslopeattwopoints,
and provides a means of correcting subsequent sample mea-
2.1 ASTM Standards:
surements,forvaluesbetweenthesetwopoints,toacalibration
E1 Specification for ASTM Thermometers
line established between the two standards employed. These
F81 Test Method for Measuring Radial Resistivity Varia-
latterstandardsmaybeofeitherknownbulkresistivityorsheet
tion on Silicon Slices
resistance;theirmaterialmustbethesameelectricaltypeasthe
F84 Test Method for Measuring Resistivity of Silicon
3 samples to be measured (see Note 8).
Slices with an In-Line Four-Point Probe
3.3.2 For subsequent measurements of bulk samples, the
F 374 Test Method for Sheet Resistance of Silicon Epi-
thickness of each sample (wafer) is measured and entered
taxial, Diffused, and Ion-Implanted Layers Using an In-
directly, or by the operator, according to the design of the
Line Four-Point Probe
instrument. These measurements are subsequently referred to
F 533 Test Method for Thickness and Thickness Variation
the standard reference plot. The corrected values are known to
of Silicon Slices
agreaterprecisionthanthoseobtainedfollowingMethodI,and
in most instances are also 23°C-equivalents.
3. Summary of Test Method
3.3.3 For subsequent measurement of thin film specimens,
3.1 There are two methods that may be used. They differ in
the sheet conductance is measured, converted to sheet resis-
calibration technique, sample measurement value range, data
tance and displayed. See 9.1.3 for relations between these
correction techniques, and suitability of instrumentation and
quantities. These measurements are subsequently referred to
are as follows:
the standard reference plot.
Methods
Factors
III
4. Significance and Use
Calibration Ascertains linearity Ascertains slope
5 samples 2 samples
4.1 Resistivityisaprimaryquantityforcharacterizationand
Sheet or bulk Sheet or bulk
specification of material used for semiconductor electronic
Application range Broad: 2 decades Narrow: 6 25 %
Sample data Direct reading, then correct Direct reading, then correct
devices. Sheet resistance is a primary quantity for character-
for temperature. for slope.
ization, specification, and monitoring of thin film fabrication
Suitable instruments Manual/Automatic Automatic: computer-
processes.
controlled
4.2 This test method requires no specimen preparation.
3.2 MethodIascertainstheconformanceoftheapparatusto
4.3 Method II is particularly well suited to computer-based
linearity and slope limits (61 digit) over a broad range (2
systems where all measurements can be quickly and automati-
decades) of calibration standard values. It qualifies apparatus
cally corrected for value offset and for temperature coefficient
for use over a wide range of sample values.
of resistivity.
3.2.1 The apparatus is first calibrated using standards of
4.4 Method I has been evaluated by interlab comparison
known resistivity or sheet resistance. Then the apparatus is
(see Section 11). Until Method II has been evaluated by
subjected to a test for linearity that involves measuring a set of
interlaboratory comparison, it is not recommended that the test
five reference specimens. As a part of the linearity test, a plot
method be used in connection with decisions between buyers
is made of the indicated values as a function of the known
and sellers.
values; two limiting curves are also plotted on the same graph.
(If all the plotted points fall within the limit curves, the
5. Interferences
apparatus is regarded as satisfactory.)
5.1 Radial resistivity variations or other resistivity nonuni-
3.2.2 For subsequent measurements of bulk samples, the
formity under the transducer are averaged by this test method
thickness of each sample (wafer) is measured and entered
in a manner which may be different from that of other types of
directly, or by the operator, according to the design of the
resistivity or sheet resistance techniques which are responsive
instrument.The conductance of the specimen is then measured
to a finite lateral area. The results may therefore differ from
by the apparatus and converted to a resistivity value that is
those of four-probe measurements depending on dopant den-
displayed. These measurements are subsequently corrected to
sity fluctuation and the four-probe spacing used.
23°C-equivalents.
NOTE 1—Test Method F81 provides a means for measuring radial
resistivity variation of silicon slices.
5.2 Uncertainty of thickness values for the reference (bulk)
Annual Book of ASTM Standards, Vol 14.03.
Annual Book of ASTM Standards, Vol 10.05. wafers can introduce, in Method I, an uncertainty in the
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Please
contact ASTM International (www.astm.org) for the latest information.
´1
F 673 – 90 (1996)
linearity plot; in Method II it can introduce a corresponding ity,ameansofzeroingtheconductancesignalintheabsenceof
uncertainty in the reference line connecting the two reference a specimen and a means for calibrating the instrument with
wafer values, if calibration is performed in resistivity values. known calibration specimens.
5.3 Uncertainty of thickness value of sample (bulk) wafers
NOTE 3—For Method I, the linearity of the apparatus is checked in an
canintroduceanerrorinbothmeasuredandreportedvaluesfor
operational qualification test (see 9.1.3).
bothMethodsIandII.Theseuncertaintiescanbeeliminatedby
NOTE 4—Atypical apparatus operates as follows. When a specimen is
executing the procedure using sheet resistance values for
inserted into the fixed gap between the two colinear sensing elements, or
reference and sample wafers. transducers,inaspecialoscillatorcircuit,eddycurrentsareinducedinthe
specimen by the alternating field between the transducers. The current
5.4 Spurious currents can be introduced in the test equip-
needed to maintain a constant voltage in the oscillator is determined
ment when it is located near high-frequency generators. If
internally; this current is a function of the specimen conductance. The
equipment is located near such sources, adequate shielding
specimen conductance is obtained by monitoring this current. Sheet
must be provided. Power line filtering may also be required.
resistance or resistivity values are obtained from the specimen conduc-
5.5 Semiconductors have a significant temperature coeffi-
tance by analog or digital electronic means; calculation of resistivity
cient of resistivity.Temperature-correction factors for extrinsic
values also requires knowledge of specimen thickness.
silicon specimens are given in Test MethodF84. Temperature
6.2 Thermometer— ASTM Precision Thermometer having
differences between any of the reference or sample wafers,
arangefrom−8to+32°Candconformingtotherequirements
during calibration or measurement, or both, will introduce a
for Thermometer 63C as specified in SpecificationE1.
measurement error in Method II.
6.3 Thickness Gage, as specified in 7.1 of Test Method
5.6 High levels of humidity may affect the indicated value.
F533 (included for completeness).
6.4 Calibration and linearity checking must be done in
6. Apparatus
consistent units, whether resistivity, sheet resistance or sheet
6.1 Electrical Measuring Apparatus, with instructions for
conductance, according to the requirements of the given
use and consisting of the following assemblies:
instrument. If resistivity values are used, knowledge of the
6.1.1 Eddy-Current Sensor Assembly, having a configura-
specimen thickness is also required. For bulk calibration or
tion of a fixed gap, between two opposed transducers, into
linearity-check specimens, the thickness is the as-measured
which a specimen slice is inserted. The assembly shall include
thickness in centimetres. For thin film specimens, the total
support(s) on which the slice rests, a device for centering the
thickness of the thin film plus substrate should be measured
slice, and a high-frequency oscillator to excite the sensing
and used; if this cannot be done, an effective thickness of
elements. The frequency of the oscillator shall be chosen to
0.0508 cm (0.020 in.) should be used. (See 9.1.3.)
provideaskindepthatleastfivetimesthethicknessoftheslice
or thin film to be measured.The skin depth is a function of the
7. Reagents and Materials
resistivity of the specimen. The assembly shall provide an
7.1 Resistivity standards or other reference specimens to
outputsignalproportionaltosheetconductance.Thisassembly
check the accuracy and linearity of the instrument. Preferably,
and associated apparatus are shown schematically in Fig. 1.
these are bulk silicon slices but may also be fabricated by ion
NOTE 2—A typical conductance apparatus is described in detail in a
implantation into silicon.
paper by Miller, Robinson, and Wiley. This paper also discusses
7.1.1 Bulk silicon standards or other reference specimens
skin-depth as a function of thickness and resistivity.
are to be measured for resistivity in accordance with Test
6.1.2 Signal Processor— Means for electronically convert-
MethodF84.The thickness of these specimens shall be within
ing, by analog or digital circuitry, the sheet conductance signal
625% of the specimens to be measured unless otherwise
to a sheet resistance value, and in the case of bulk substr
...
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