ASTM F1392-00

Standard Test Method for Determining Net Carrier Density Profiles in Silicon Wafers by Capacitance-Voltage Measurements With a Mercury Probe

SCOPE
1.1 This test method  covers the measurement of net carrier density and net carrier density profiles in epitaxial and polished bulk silicon wafers in the range from about 4 X 10 13  to about 8 X 10 16  carriers/cm  (resistivity range from about 0.1 to about 100 [omega][dot]cm in -type wafers and from about 0.24 to about 330 [omega][dot]cm in -type wafers).
1.2 This test method requires the formation of a Schottky barrier diode with a mercury probe contact to an epitaxial or polished wafer surface. Chemical treatment of the silicon surface may be required to produce a reliable Schottky barrier diode (1).  The surface treatment chemistries are different for - and -type wafers. This test method is sometimes considered destructive due to the possibility of contamination from the Schottky contact formed on the wafer surface; however, repetitive measurements may be made on the same test specimen.
1.3 This test method may be applied to epitaxial layers on the same or opposite conductivity type substrate. This test method includes descriptions of fixtures for measuring substrates with or without an insulating backseal layer.
1.4 The depth of the region that can be profiled depends on the doping level in the test specimen. Based on data reported by Severin (1) and Grove (2), Fig. 1 shows the relationships between depletion depth, dopant density, and applied voltage together with the breakdown voltage of a mercury silicon contact. The test specimen can be profiled from approximately the depletion depth corresponding to an applied voltage of 1 V to the depletion depth corresponding to the maximum applied voltage (200 V or about 80% of the breakdown voltage, whichever is lower). To be measured by this test method, a layer must be thicker than the depletion depth corresponding to an applied voltage of 2 V.
1.5 This test method is intended for rapid carrier density determination when extended sample preparation time or high temperature processing of the wafer is not practical.  Note 1-Test Method F419 is an alternative method for determining net carrier density profiles in silicon wafers from capacitance-voltage measurements. This test method requires the use of one of the following structures: ( ) a gated or ungated p-n junction diode fabricated using either planar or mesa technology or ( ) an evaporated metal Schottky diode.
1.6 This test method provides for determining the effective area of the mercury probe contact using polished bulk reference wafers that have been measured for resistivity at 23°C in accordance with Test Method F84 (Note 2). This test method also includes procedures for calibration of the apparatus for measuring both capacitance and voltage.  Note 2-An alternative method of determining the effective area of the mercury probe contact that involves the use of reference wafers whose net carrier density has been measured using fabricated mesa or planar p-n junction diodes or evaporated Schottky diodes is not included in this test method but may be used if agreed upon by the parties to the test.
1.7 This standard does not purport to address all of the safety problems, 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 7.1 (Note 4), 7.2, 7.10.3 (Note 8), 8.2, 11.5.1 (Note 18), 11.6.3, and 11.6.5.

General Information

• Status: Historical
• Publication Date: 09-Jun-2000
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics

Relations

• Replaced By: ASTM F1392-02 - Standard Test Method for Determining Net Carrier Density Profiles in Silicon Wafers by Capacitance-Voltage Measurements With a Mercury Probe (Withdrawn 2003)
• Effective Date: 10-Dec-2002

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 1392 – 00
Standard Test Method for
Determining Net Carrier Density Profiles in Silicon Wafers
by Capacitance-Voltage Measurements With a Mercury
Probe
This standard is issued under the fixed designation F 1392; 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.
1. Scope voltage (200 V or about 80 % of the breakdown voltage,
whichever is lower). To be measured by this test method, a
1.1 This test method covers the measurement of net carrier
layer must be thicker than the depletion depth corresponding to
density and net carrier density profiles in epitaxial and polished
an applied voltage of 2 V.
bulk silicon wafers in the range from about 4 3 10 to about
16 3
1.5 This test method is intended for rapid carrier density
8 3 10 carriers/cm (resistivity range from about 0.1 to
determination when extended sample preparation time or high
about 100 V·cm in n-type wafers and from about 0.24 to about
temperature processing of the wafer is not practical.
330 V·cm in p-type wafers).
1.2 This test method requires the formation of a Schottky
NOTE 1—Test Method F 419 is an alternative method for determining
barrier diode with a mercury probe contact to an epitaxial or
net carrier density profiles in silicon wafers from capacitance-voltage
measurements. This test method requires the use of one of the following
polished wafer surface. Chemical treatment of the silicon
structures: (1) a gated or ungated p-n junction diode fabricated using either
surface may be required to produce a reliable Schottky barrier
3 planar or mesa technology or ( 2) an evaporated metal Schottky diode.
diode (1). The surface treatment chemistries are different for
n- and p-type wafers. This test method is sometimes considered 1.6 This test method provides for determining the effective
area of the mercury probe contact using polished bulk refer-
destructive due to the possibility of contamination from the
Schottky contact formed on the wafer surface; however, ence wafers that have been measured for resistivity at 23°C in
accordance with Test Method F 84 (Note 2). This test method
repetitive measurements may be made on the same test
specimen. also includes procedures for calibration of the apparatus for
measuring both capacitance and voltage.
1.3 This test method may be applied to epitaxial layers on
the same or opposite conductivity type substrate. This test
NOTE 2—An alternative method of determining the effective area of the
method includes descriptions of fixtures for measuring sub-
mercury probe contact that involves the use of reference wafers whose net
strates with or without an insulating backseal layer.
carrier density has been measured using fabricated mesa or planar p-n
1.4 The depth of the region that can be profiled depends on junction diodes or evaporated Schottky diodes is not included in this test
method but may be used if agreed upon by the parties to the test.
the doping level in the test specimen. Based on data reported
by Severin (1) and Grove (2), Fig. 1 shows the relationships
1.7 This standard does not purport to address all of the
between depletion depth, dopant density, and applied voltage
safety concerns, if any, associated with its use. It is the
together with the breakdown voltage of a mercury silicon
responsibility of the user of this standard to establish appro-
contact. The test specimen can be profiled from approximately
priate safety and health practices and determine the applica-
the depletion depth corresponding to an applied voltage of 1 V
bility of regulatory limitations prior to use. Specific hazard
to the depletion depth corresponding to the maximum applied
statements are given in 7.1, ( 7.2, 7.10.3 (Note 7), 8.2, 11.5.1,
11.6.3, and 11.6.5.
2. Referenced Documents
This test method is under the jurisdiction of ASTM Committee F-1 on
2.1 ASTM Standards:
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon
D 5127 Guide for Ultra Pure Water Used in the Electronics
Materials and Process Control.
Current edition approved June 10, 2000. Published August 2000. Originally
and Semiconductor Industry
published as F 1392 – 92. Last previous edition F 1392 – 93.
D 4356 Practice for Establishing Consistent Test Method
DIN 50439, Determination of the Dopant Concentration Profile of a Single
Tolerances
Crystal Semiconductor Material by Means of the Capacitance-Voltage Method and
Mercury Contact, is technically equivalent to this test method. DIN 50439 is the E 691 Practice for Conducting an Interlaboratory Study to
responsibility of DIN Committee NMP 221, with which Committee F-1 maintains
close liaison. DIN 50439 is available from Beuth Verlag GmbH, Burggrafenstraße
4-10, D-1000, Berlin 30, Germany.
3 4
The boldface numbers in parentheses refer to the list of references at the end of Annual Book of ASTM Standards, Vol 11.01.
this test method. Annual Book of ASTM Standards, Vol 14.02.
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 1392 – 00
(a) Depletion Depth as a Function of Dopant Density with Applied Reverse Bias Voltage as a Parameter.
(b) Applied Reverse Bias Voltage as a Function of Dopant Density with Depletion as a Parameter.
NOTE 1—The light dashed line represents the applied reverse bias voltage at which breakdown occurs in a mercury-silicon contact; the heavy dashed
line represents 80 % of this voltage, it is recommended that the applied reverse bias voltage not exceed this value. The light chain-dot line represents the
maximum reverse bias voltage specified in this test method.
FIG. 1 Relationships Between Depletion Depth, Applied Reverse Bias Voltage, and Dopant Density
Determine the Precision of a Test Method F 81 Test Method for Measuring Radial Resistivity Varia-
F 26 Test Methods for Determining the Orientation of a
tion on Silicon Wafers
Semiconductive Single Crystal
F 84 Test Method for Measuring Resistivity of Silicon
F 42 Test Methods for Conductivity Type of Extrinsic 6
Wafers with an In-Line Four-Point Probe
Semiconducting Materials
F 419 Test Method for Determining Carrier Density in
Silicon Epitaxial Layers by Capacitance-Voltage Measure-
ments on Fabricated Junction or Schottky Diodes
Annual Book of ASTM Standards, Vol 10.05.
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 1392 – 00
F 672 Test Method for Measuring Resistivity Profiles Per- mercury probe contact is reverse biased and the low-resistance
pendicular to the Surface of a Silicon Wafer Using a return contact is forward biased.
Spreading Resistance Probe 4.6 The net carrier density profile (net carrier density as a
F 723 Practice for Conversion Between Resistivity and function of depth from the surface) is calculated from the
Dopant Density for Boron-Doped, Phosphorus-Doped, and measured values of capacitance and applied voltage by one of
Arsenic-Doped Silicon two equivalent methods.
F 1153 Test Method for Characterization of Metal-Oxide-
NOTE 3—Net carrier density values obtained by this test method are
Silicon (MOS) Structures by Capacitance-Voltage Mea-
often converted to resistivity, which is generally a more familiar parameter
surements
in the industry. If this is done, the conversion should be made in
F 1241 Terminology of Silicon Technology
accordance with the computational methods given in 7.2 of Practice F 723
(conversion from dopant density to resistivity). Note that in applying this
2.2 SEMI Standards:
conversion procedure in either direction it is assumed that the net carrier
SEMI C28 Specifications for Hydrofluoric Acid
7 density is equal to the dopant density.
SEMI C29 Specification for Hydrofluoric Acid, 4.9 %
SEMI C30 Specification for Hydrogen Peroxide
5. Significance and Use
5.1 This test method can be used for research and develop-
3. Terminology
ment, process control, and materials specification, evaluation,
3.1 Definitions:
and acceptance purposes. However, in the absence of interlabo-
3.1.1 For definitions of terms used in silicon wafer technol-
ratory test data to establish its reproducibility, this test method
ogy refer to Terminology F 1241.
should be used for materials specification and acceptance only
3.1.2 Definitions of the statistical terms repeatability and
after the parties to the test have established reproducibility and
reproducibility are given in Practice E 691.
correlation.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 compensation capacitance, C — the sum of the
comp
6. Interferences
stray capacitance of the measurement system and the periph-
6.1 A poor Schottky contact, which is generally indicated by
eral capacitance of the mercury probe contact (see 10.3).
an excessively high leakage current (see 11.5) is the most
3.2.2 low-resistance contact—an electrically and mechani-
common problem in capacitance-voltage measurements made
cally stable contact (3) in which the resistance across the
with mercury probe instruments. It must be emphasized that
contact does not result in excessive series resistance as
the use of a poor Schottky contact does not actually prevent a
determined in 11.4 (see also 6.4).
carrier density determination but produces an erroneous result.
3.2.2.1 Discussion—a low-resistance contact may usually
6.2 Improper determination of the compensation capaci-
be achieved by using a metal-semiconductor contact with an
tance, C , (see 10.3) can cause significant errors in the
area much larger than that of the mercury probe contact. comp
capacitance measurement. In homogeneous material, improper
3.2.3 mercury probe contact—a Schottky barrier diode
zeroing or use of an improper value for C results in an
formed by bringing a column of mercury into contact with an comp
apparent monotonic increase or decrease of carrier density with
appropriately prepared polished or epitaxial silicon surface.
distance from the Schottky barrier. In some fixtures, inherently
4. Summary of Test Method large stray capacitances exist; in such cases, the value of C
comp
may depend both on the diameter of the wafer and on the
4.1 The compensation capacitance and effective mercury
position of the wafer on the chuck. If these dependencies are
probe contact area are determined using a reference wafer.
observed, they may be reduced or eliminated by shielding the
4.2 The test specimen is placed in the mercury probe fixture.
mercury probe column. If shielding is not practical, probe
A column of mercury is brought into contact with the epitaxial
calibration procedures should be carried out with wafers of the
or polished surface of the specimen by a pressure differential
same diameter as the wafers being tested and care should be
between the mercury and ambient to form a Schottky barrier
taken to ensure that the geometry of wafer and probe is the
diode (mercury probe contact).
same during calibration and measurement.
4.3 A low-resistance return contact is also made to either the
6.3 Alternating frequency test signals greater than 0.05 V
front or back surface of the wafer. This contact may be either
rms may lead to errors in the measured capacitance.
a metal plate or a second mercury-silicon contact with an area
6.4 Excessive series resistance in the capacitance measure-
much larger than the mercury probe contact.
ment circuit can cause significant errors in the measured
4.4 The quality of the Schottky barrier diode formed by the
capacitance values. Series resistance values greater than 1 kV
mercury probe contact is evaluated by measuring its series
have been reported to cause measurement error in some cases
resistance and its reverse current characteristics.
(4, 5). The primary source of excessive series resistance is
4.5 The small-signal, high frequency capacitance of the
generally a high-resistance return contact; other possible
mercury probe contact is measured as a function of the voltage
sources are bulk resistance in the wafer and wiring defects in
applied between the mercury probe column and the return
the mercury probe fixture or the test cables (see 11.4).
contact. The polarity of the applied voltage is such that the
6.5 When exposed to air, a scum tends to form on the
exposed surface of the mercury used to form the mercury probe
7 contact. When freed from the surface, this scum floats to the
Available from Semiconductor Equipment and Materials International, 805
East Middlefield Road, Mountain View, CA 94043. top of the mercury column. It is necessary to make certain that
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 1392 – 00
the mercury that contacts the wafer surface is clean by sustaining an external d-c bias of up to 200 V. Provision shall
changing the mercury periodically or by otherwise removing be made to compensate a compensation capacitance of up to 10
the scum from the exposed surface. pF.
6.6 A dirty or damaged capillary tube containing the mer-
NOTE 4—Capacitance meters or bridges capable of measuring the phase
cury column may also result in unstable measurements (see
angle, equivalent series resistance, conductance or total impedance in
10.4.2.2).
addition to the capacitance may be used.
6.7 If the reference wafer is not sufficiently uniform
NOTE 5—Capacitance meters with nominal frequencies from 100 kHz
throughout its thickness, the value of net carrier density, N ,
to 1 MHz have been used for measurements of the type covered by this
ref
test method. If an instrument with a nominal frequency other than 1 MHz
determined by the four-point probe measurement (see 8.4.3)
is employed, the user shall demonstrate that it obtains results equivalent to
may differ from the value of net carrier density at the surface
the specified instrument.
where the mercury probe measurement is made. Use of
erroneous values of N results in incorrect values for effective
7.4 Dc Power Supply, continuously variable from 0 V to the
ref
probe contact area (see 10.3). Further, if the resistivity profile
maximum expected reverse bias (Note 6) or 200 V, whichever
of the reference wafer is not uniform near the surface, an
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