ASTM F672-88(1995)e1

Standard Test Method for Measuring Resistivity Profiles Perpendicular to the Surface of a Silicon Wafer Using a Spreading Resistance Probe

SCOPE
1.1 This test method covers measurement of the resistivity profile perpendicular to the surface of a silicon wafer of known orientation and type.
Note 1--This test method may also be applicable to other semiconductor materials, but feasibility and precision have been evaluated only for silicon and germanium.
1.2 This test method may be used on epitaxial films, substrates, diffused layers, or ion-implanted layers, or any combination of these.
1.3 This test method is comparative in that the resistivity profile of an unknown specimen is determined by comparing its measured spreading resistance value with those of calibration standards of known resistivity. These calibration standards must have the same surface preparation, conductivity type, and crystallographic orientation as the unknown specimen.
1.4 This test method is intended for use on silicon wafers in any resistivity range for which there exist suitable standards. Polished, lapped, or ground surfaces may be used.
1.5 This test method is destructive in that the specimen must be beveled.
1.6 Correction factors, which take into account the effects of boundaries or local resistivity variations with depth, are needed prior to using calibration data to calculate resistivity from the spreading resistance values.
Note 2--This test method extends Method F525 to depth profiling.
Note 3--This test method provides means for directly determining the resistivity profile of a silicon specimen normal to the specimen surface. Unlike Test Methods F84, F374, F1392, and F1393, it can provide lateral spatial resolution of resistivity on the order of a few micrometres, and an in-depth spatial resolution on the order of 10 nm (100 A). This test method can be used to profile through  p-n junctions.
1.7 This test method is primarily a measurement for determining the resistivity profile in a silicon wafer. However, common practice is to convert the resistivity profile information to a density profile. For such purposes, a conversion between resistivity and majority carrier density is provided in Appendix X2.
1.8 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 9.

General Information

• Status: Historical
• Publication Date: 09-Jun-2001
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics

Relations

• Replaced By: ASTM F672-01 - Standard Test Method for Measuring Resistivity Profiles Perpendicular to the Surface of a Silicon Wafer Using a Spreading Resistance Probe (Withdrawn 2003)
• Effective Date: 10-Jun-2001

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn. Contact ASTM International (www.astm.org) for the latest information.
e1
Designation: F 672 – 88 (Reapproved 1995)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Measuring Resistivity Profiles Perpendicular to the Surface
of a Silicon Wafer Using a Spreading Resistance Probe
This standard is issued under the fixed designation F 672; 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.
e NOTE—Keywords were added editorially in January 1995.
INTRODUCTION
The measurement of resistivity profile by means of a spreading resistance probe is a complex
procedure, with a number of commonly accepted options for carrying out the component measure-
ments. ASTM Committee F-1 on Electronics has designed this test method to allow a range of choices,
consistent with good practice, for the electronic configuration, type of specimen preparation, and
method for measuring bevel angle. Items not specified by this test method are to be agreed upon by
the parties to the test, usually from a specified set of choices in the context of a general restriction. The
measurement of bevel angle is particularly difficult to specify, as the selection of an appropriate
method depends not only on the range of angle measured but also on the quality of the instrumentation
available for that method. Although ideally the beveled surface and the original surface should be two
planes intersecting along a straight line, the actual geometry may differ from this ideal, further
complicating the measurement. These points are recognized in the section on interferences and in
Appendix X1 and associated references on the bevel-angle measurement.
1. Scope 1.6 Correction factors, which take into account the effects of
boundaries or local resistivity variations with depth, are needed
1.1 This test method covers measurement of the resistivity
prior to using calibration data to calculate resistivity from the
profile perpendicular to the surface of a silicon wafer of known
spreading resistance values.
orientation and type.
NOTE 1—This test method may also be applicable to other semicon-
NOTE 2—This test method extends Method F 525 to depth profiling.
ductor materials, but feasibility and precision have been evaluated only for
NOTE 3—This test method provides means for directly determining the
silicon and germanium.
resistivity profile of a silicon specimen normal to the specimen surface.
1.2 This test method may be used on epitaxial films, Unlike Method F 84 and Test Methods F 374 and F 419, it can provide
lateral spatial resolution of resistivity on the order of a few micrometres,
substrates, diffused layers, or ion-implanted layers, or any
˚
and an in-depth spatial resolution on the order of 10 nm (100 A). This test
combination of these.
method can be used to profile through p-n junctions.
1.3 This test method is comparative in that the resistivity
profile of an unknown specimen is determined by comparing
1.7 This test method is primarily a measurement for deter-
its measured spreading resistance value with those of calibra-
mining the resistivity profile in a silicon wafer. However,
tion standards of known resistivity. These calibration standards
common practice is to convert the resistivity profile informa-
must have the same surface preparation, conductivity type, and
tion to a density profile. For such purposes, a conversion
crystallographic orientation as the unknown specimen.
between resistivity and majority carrier density is provided in
1.4 This test method is intended for use on silicon wafers in
Appendix X2.
any resistivity range for which there exist suitable standards.
1.8 This standard does not purport to address all of the
Polished, lapped, or ground surfaces may be used.
safety concerns, if any, associated with its use. It is the
1.5 This test method is destructive in that the specimen must
responsibility of the user of this standard to establish appro-
be beveled.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. Specific hazard
statements are given in Section 9.
This test method is under the jurisdiction of ASTM Committee F-1 on
Electronicsand is the direct responsibility of Subcommittee F01.06 on Silicon
Material and Process Control.
2. Referenced Documents
Current edition approved Oct. 31, 1988. Published December 1988. Originally
published as F672 – 80. Last previous edition F672 – 87. 2.1 ASTM Standards:
F 672
D 1125 Test Methods for Electrical Conductivity and Re- resistivity gradients or electrical boundaries, this ratio also
sistivity of Water includes an effect due to those gradients or boundaries.
E 1 Specification for ASTM Thermometers 3.1.4.2 Discussion—In a three-probe arrangement, the
F 26 Test Methods for Determining the Orientation of a experimental conditions approximate those of the definition
Semiconductive Single Crystal (based on a single probe) and the spreading resistance is given
F 42 Test Method for Conductivity Type of Extrinsic Semi- by
conducting Materials
R 5 V/I
s
F 84 Test Method for Measuring Resistivity of Silicon
(2)
Slices with an In-Line Four-Point Probe
where:
F 374 Test Method for Sheet Resistance of Silicon Epi-
V 5 potential drop between one of the current-carrying
taxial, Diffused, Polysilicon, and Ion-Implanted Layers
4 probes and the reference (non-current-carrying) probe
Using an In-Line Four-Point Probe
on the front surface, mV, and
F 419 Test Method for Net Carrier Density in Silicon
I 5 current through the metal probe, mA.
Epitaxial Layers by Capacitance Voltage Measurements on
4 In a two-probe arrangement, the potential drop, V, is measured
Fabricated Junction Schottky Diodes
between two similar current-carrying metal probes. In this
F 525 Test Method for Measuring Resistivity of Silicon
4 case, the voltage-to-current ratio, and hence the spreading
Wafers Using a Spreading Resistance Probe
resistance, is approximately twice that associated with a single
F 674 Practice for Preparing Silicon for Spreading Resis-
4 probe.
tance Measurements
3.1.5 substrate—in semiconductor technology, a wafer
F 723 Practice for Conversion Between Resistivity and
which is the basis for subsequent processing operations in the
Dopant Density for Boron-Doped and Phosphorus-Doped
4 fabrication of semiconductor devices or circuits.
Silicon
3.1.5.1 Discussion—The devices or circuits may be
3. Terminology
fabricated directly in the substrate or in a film of the same or
another material grown or deposited on the substrate.
3.1 Definitions of Terms Specific to This Standard:
3.1.1 conducting boundary— for the purposes of this test
4. Summary of Test Method
method, a boundary between two specimen layers of the same
4.1 A portion of the specimen wafer is beveled at an angle.
conductivity type taken to be the point at which the spreading
The spreading resistance of a reproducibly formed point
resistance increases to twice the local minimum value it has in
pressure contact (or contacts) is measured at a sequence of
the layer of lower resistivity (Fig. 1a).
locations on the beveled surface. The spreading resistance may
3.1.2 effective electrical contact radius, a (cm)—of a
be measured using two, or three, probes (1) by applying a
spreading resistance probe assembly, an empirical quantity
known constant voltage and measuring the current, (2)by
defined by
applying a known constant current and measuring the voltage,
a 5 nr /4R (1)
~ !
s
or (3) by using a resistance comparator technique. A correction
factor must be used (1, 2, 3) which takes into account the
where:
effect of local resistivity gradients and boundaries on the finite
n 5 number of current-carrying probes across which
sampling volume of the probes. The resistivity of the material
the potential drop is determined,
immediately under the probes is then determined from a
r5 resistivity of a homogeneous semiconductor
calibration curve derived from spreading resistance
specimen, V·cm, and
measurements made under the same conditions on calibration
R 5 measured spreading resistance, V.
s
standards of known resistivity.
3.1.2.1 Discussion—For a three-probe arrangement, n 5 1;
4.2 The following quantities are not specified by this test
for a two-probe arrangement, n 5 2.
method and shall be agreed upon by the parties to the test:
3.1.3 insulating boundary—for the purposes of this test
4.2.1 Probe spacing, μm (7.3.1.3),
method, a boundary between two specimen layers of opposite
4.2.2 Sampling plan (10.1,
conductivity type, taken to be the point at which the local
4.2.3 Minimum bevel length, mm, if required (11.1.1),
maximum of the spreading resistance occurs (Fig. 1b).
4.2.4 Bevel angle, deg, appropriate to the total depth of
3.1.4 spreading resistance, R (V)—of a semiconductor, the
s
interest and desired resolution of the test specimen data (11.3
ratio of (1) the potential drop between a small-area conductive
and Table 1),
metal probe, and a reference point on the semiconductor, to ( 2)
4.2.5 Beveling technique (11.6),
the current through the probe.
4.2.6 Method for obtaining calibration curve (13.4),
3.1.4.1 Discussion—This ratio, in fact, measures metal to
4.2.7 Method for measuring bevel angle (14.10),
semiconductor contact resistance as well as classical spreading
4.2.8 Probe spacing and probe step increment, μm,
resistance for a homogeneous specimen without electrical
appropriate to the resolution desired along the profile of
boundaries in the vicinity of the probes. For a specimen having
interest (13.2, 14.4),
Annual Book of ASTM Standards, Vol 11.01.
3 5
Annual Book of ASTM Standards, Vol 14.03. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 10.05. this test method.
F 672
4.2.9 Algorithm for sampling volume correction factor exposed to an aqueous solution may be erratic and
(15.4), and nonreproducible. Surfaces exposed to solutions containing
4.2.10 Conversion from resistivity profile to carrier density fluorine ions may also exhibit instability. The heat treatment
profile (see Appendix X3). included in the procedure (see 11.8) has been found to reduce
these instabilities for p-type specimens (5, 6).
NOTE 4—Information relating the depth resolution and bevel angle for
6.7.2 Surface Damage—Spreading resistance
probe step increments of 5 and 10 μm and also bevel length to the layer
thickness and bevel angle is given in Table 1. The probe step increment measurements made in areas of severe or nonuniform
should be larger than the diameter of the specimen area damaged by the
mechanical damage may give erroneous results. Such damage
probes.
may be caused by previous spreading resistance probe marks,
NOTE 5—Model data, of the type used to qualify participants in the
or by improper surface preparation.
round robin is provided in Annex A1. These are idealized data, free of
6.7.3 High Impurity Concentration—At impurity
measurement noise and contact calibration nonlinearity. They may be used
20 −3
concentrations greater than approximately 10 cm the
to study the effects on a calculated resistivity profile of data round-off
error or input measurement noise (if random or systematic noise is added defects caused by the impurity may have an effect on the
to the model data). While they may be used to compare the results from
measured spreading resistance. These defects and consequent
different algorithms, such comparisons may be misleading. It has been
effects may not be the same for all heavily doped specimens.
found that some algorithms do a highly satisfactory analysis of certain real
6.7.4 Imperfect Bevel—An ideal beveled surface is planar
structures despite their relatively poorer performance on model data as
and intersects sharply along a straight line with a planar
described in Annex A1, (4). This is thought to be due to their relatively
original surface of the specimen. Deviations from an ideal
better ability to deal with measurement noise and with probe calibration
nonlinearity. bevel can be caused by a number of factors such as nonuniform
specimen thickness, specimen warp during mounting on the
5. Significance and Use
beveling block, rocking of the specimen mount during
5.1 This test method can be used for process control,
beveling, flexing or compression of the plate against which the
research and development, and materials acceptance purposes.
beveling is done, and preferential attack of the beveling
medium at the edge of the bevel. A non-ideal bevel may cause
6. Interferences
an incorrect bevel angle to be measured, present a changing
6.1 Temperature—If the calibration and specimen
depth scale along the line scanned by the probes, or both. Two
measurements are not made at the same temperature, the
simple limiting-case beveling defects can be described.
accuracy of the results is likely to be adversely affected, as
6.7.4.1 Bevel edge rounding is shown in Fig. 2. It is
spreading resistance measurements are sensitive to the
characterized by a gradual transition between the original and
temperature of the specimen.
beveled surfaces of the specimen. It is found more likely to
6.2 Light—Photoconductive and photovoltaic effects can
occur when a chem-mechanical beveling process is used, when
seriously influence the resistance determined by this test
a reciprocating motion is used during beveling, or when too
method, especially on wafers having p-n junctions.
soft a material is used for the polishing plate. Its existence is
6.3 Radiofrequency Fields—If the apparatus is located near
difficult to recognize by casual observation. Its presence can be
unshielded radiofrequency sources, the precision and accuracy
seen, in general, when using bevel measurement methods 1, 3,
of the results may be adversely affected, as spurious currents
or 4 in Appendix X1. The effect of this defect can be reduced
can be introduced in the measurement circuit in the presence of
if the specimen is covered with an oxide or nitride layer prior
high-frequency fields.
to beveling.
6.4 Mechanical Vibration—If the apparatus is not
6.7.4.2 Bevel edge arcing is shown in Fig. 3. It is
sufficiently isolated from building-induced or other vibration
characterized by a curved or arced intersection of the original
sources, the precision and accuracy of the results may be
and beveled surfaces of the specimen, indicating that one or
adversely affected, as the probes are delicate (the entire probe
both surfaces are non-planar. Howev
...