ASTM F398-92(1997)

Standard Test Method for Majority Carrier Concentration in Semiconductors by Measurement of Wavenumber or Wavelength of the Plasma Resonance Minimum

SCOPE
1.1 This test method covers determination of the wavenumber of the plasma resonance minimum in the infrared reflectance of a doped semiconductor specimen, from which the majority carrier concentration can be obtained.  
1.2 This test method of determination of the wavenumber minimum is nondestructive and contactless. It is applicable to n- and p-type silicon, n- and p-type gallium arsenide, and n-type germanium.  
1.3 This test method gives a relative measurement in that the relation between the wavenumber of the plasma resonance minimum and the majority carrier concentration is empirical. Such relations have been established for the several cases summarized in Annex A1. These relations are based upon determinations of the plasma resonance minimum by the procedure of this method and determinations of the Hall coefficient according to Test Methods F76 (Section 2) or resistivity according to Test Methods F43 or Test Method F84 (Section 2) as appropriate.  
1.4 These relations have been established over a majority carrier concentration range from 1.5 X 10   to 1.5 X 10   cm   for n-type silicon, from 3 X 10   to 5 X 10   for p-type silicon, from 3 X 10   to 7 X 10   for n-type germanium, from 1.5 X 10   to 1 X 10   for n-type gallium arsenide, and from 2.6 X 10   to 1.3 X 10   cm   for p-type gallium arsenide.  
1.5 These relations can be extended or developed for other materials by measuring the wavelength of the plasma resonance minimum according to this procedure on specimens whose majority carrier concentration has been determined by other means.  
1.6 This test method is applicable to both bulk and diffused material. However, since there is some controversy over the effects of variations of junction depth on the measurement, it should be applied to surface concentration measurements on shallow (1 [mu]m or less) diffusions only on a relative basis unless there is experimental corroboration of the results under the conditions of interest.  
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.

General Information

• Status: Historical
• Publication Date: 09-Jun-1997
• Technical Committee: F01 - Electronics

Relations

• Replaced By: ASTM F398-92(2002) - Standard Test Method for Majority Carrier Concentration in Semiconductors by Measurement of Wavenumber or Wavelength of the Plasma Resonance Minimum (Withdrawn 2003)
• Effective Date: 15-May-1992

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 398 – 92 (Reapproved 1997)
Standard Test Method for
Majority Carrier Concentration in Semiconductors by
Measurement of Wavenumber or Wavelength of the Plasma
Resonance Minimum
This standard is issued under the fixed designation F 398; 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.
INTRODUCTION
As originally published, this test method was written for infrared instruments with output in units
of wavelength. Calibration data, as included, were based on infrared measurements in units of
wavelength and on a combination of concentration scale methods including Hall effect, neutron
activation analysis, and four-probe resistivity. These latter measurements were converted, using the
empirical data of Irvin, from resistivity to “impurity concentration.” The result of this procedure is
calibration data that is a mixture of carrier concentration and impurity concentration values. While the
differences between them is large only at very high concentrations, there are values in the original
calibration plots for silicon (Fig. A1.1 and Fig. A1.2) that are above currently accepted solid-solubility
limit values.
Common practice current infrared spectrophotometers is to give output in units of wavenumbers
−1
(cm ). In order to relate this test method and its original calibration to current infrared units without
introducing numerical error (the calibration relation is not analytically invertible to wavenumbers), the
direct substitution of 10 000/wavenumber for wavelength is given in the analysis equation and in the
tables of coefficients.
This test method is not believed to have wide current use in the semiconductor industry. However,
because this test method may be useful for some applications and because the calibration data
contained herein is believed to be available nowhere else in the archival literature, this test method is
being retained as a standard.
1. Scope procedure of this method and determinations of the Hall
coefficient according to Test Methods F 76 (Section 2) or
1.1 This test method covers determination of the wavenum-
resistivity according to Test Methods F 43 or Test Method F 84
ber of the plasma resonance minimum in the infrared reflec-
(Section 2) as appropriate.
tance of a doped semiconductor specimen, from which the
1.4 These relations have been established over a majority
majority carrier concentration can be obtained.
18 21
carrier concentration range from 1.5 3 10 to 1.5 3 10
1.2 This test method of determination of the wavenumber
−3 18 20
cm for n-type silicon, from 3 3 10 to 5 3 10 for p-type
minimum is nondestructive and contactless. It is applicable to
18 19
silicon, from 3 3 10 to 7 3 10 for n-type germanium, from
n- and p-type silicon, n- and p-type gallium arsenide, and
17 19
1.5 3 10 to 1 3 10 for n-type gallium arsenide, and from
n-type germanium.
18 20 −3
2.6 3 10 to 1.3 3 10 cm for p-type gallium arsenide.
1.3 This test method gives a relative measurement in that
1.5 These relations can be extended or developed for other
the relation between the wavenumber of the plasma resonance
materials by measuring the wavelength of the plasma reso-
minimum and the majority carrier concentration is empirical.
nance minimum according to this procedure on specimens
Such relations have been established for the several cases
whose majority carrier concentration has been determined by
summarized in Annex A1. These relations are based upon
other means.
determinations of the plasma resonance minimum by the
1.6 This test method is applicable to both bulk and diffused
material. However, since there is some controversy over the
This test method is under the jurisdiction of ASTM Committee F01 on
effects of variations of junction depth on the measurement, it
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon
should be applied to surface concentration measurements on
Materials and Process Control.
shallow (1 μm or less) diffusions only on a relative basis unless
Current edition approved May 15, 1992. Published July 1992. Originally
e1
published as F 398 – 74 T. Last previous edition F 398 – 87 .
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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 398
there is experimental corroboration of the results under the 5. Significance and Use
conditions of interest.
5.1 The measurement of the carrier concentration of a
1.7 This standard does not purport to address all of the
semiconductor is a vital part of the development and manufac-
safety concerns, if any, associated with its use. It is the
ture of semiconductor devices and integrated circuits.
responsibility of the user of this standard to establish appro-
5.2 An important use of this technique is the measurement
priate safety and health practices and determine the applica-
of the surface concentration of diffused layers. There is,
bility of regulatory limitations prior to use.
however, some controversy about the effect of variation of
junction depth on the correspondence between the concentra-
2. Referenced Documents
tion measured by this technique and the true concentration,
2.1 ASTM Standards:
particularly for very shallow (1 μm or less) junctions.
E 275 Practice for Describing and Measuring Performance
5.3 This technique also may be applied to the measurement
of Ultraviolet, Visible, and Near Infrared Spectrophotom-
of bulk materials and to the study of nonuniformities across the
eters
surface of those materials. For such application the user should
F 42 Test Methods for Conductivity Type of Extrinsic
be certain that the surfaces are free of the films which normally
Semiconducting Materials
appear on an as-grown crystal.
F 43 Test Methods for Resistivity of Semiconductor Mate-
5.4 It must be noted that the reflectivity minimum measured
rials
by this procedure and associated with the plasma resonance
F 76 Test Methods for Measuring Resistivity and Hall
occurs at a larger wavenumber value than that associated with
Coefficient and Determining Hall Mobility in Single-
the actual plasma resonance. The latter occurs at a wavenumber
Crystal Semiconductors
value which can be calculated from the equation:
F 84 Test Method for Measuring Resistivity of Silicon
2 2 2
Slices with an In-Line Four-Point Probe
5l 5 ~2p c! m*e/Ne
S D P
n
P
3. Terminology
where:
−1
3.1 Definitions of Terms Specific to This Standard:
n = wavenumber value of plasma resonance, m ,
P
3.1.1 plasma resonance—plasma resonance is the transition
l = wavelength of plasma resonance, m,
P
between low-frequency and high-frequency reflectivity condi-
c = speed of light, m/s,
m* = effective mass of free carriers, kg,
tions in an extrinsic semiconductor in which the mobile carriers
e = low frequency dielectric constant, F/m,
and the immobile ionized impurities can be considered as a
−3
N = density of free carriers, m , as measured by this
plasma. At high frequencies or short wavelengths, the fields are
method, and
varying too fast for the plasma to respond and the reflectivity
e = electronic charge, C.
approaches that of intrinsic silicon. At low frequencies or long
wavelengths, the fields vary slowly so that the plasma may
6. Interferences
respond and the reflectivity is high.
3.1.2 plasma resonance minimum—this is the minimum in 6.1 Highly polished surfaces can be obtained over highly
reflectivity as a function of wavenumber associated with
damaged regions; this can cause misleading results. Users of
plasma resonance. this method should, therefore, assure themselves that the
polishing technique that they are using yields damage-free
4. Summary of Test Method
surfaces in order to be certain that the measurement obtained
4.1 The majority carrier concentration of a semiconductor is
using this technique represents the bulk properties of the
measured by determining the reflectivity of the semiconductor
materials.
as a function of wavenumber in the infrared region of the
NOTE 1—Pending establishment of a method of test for surface damage,
spectrum. This reflectivity has a high-wavenumber value
the user may check for surface damage by successively measuring the
which is almost independent of carrier concentration and is
reflectivity spectrum of the specimen and chemically removing a layer
characteristic of the intrinsic semiconductor lattice. As the
from the surface using a non-preferential etchant until the plasma
wavenumber decreases, the reflectivity decreases to a mini- resonance readings from successive measurements agree.
mum at a wavenumber, n which is characteristic of the
PR
6.2 Since specimens may be inhomogeneous, users of this
number of free carriers in the semiconductor. For decreasing
technique for a referee method should agree on the location on
wavenumbers, beyond n , the reflectivity increases rapidly,
PR
each specimen where the measurement is to be taken.
approaching a value of unity.
6.3 Anomalously low mobility material may yield a mea-
4.2 Carrier concentration in a specimen of unknown doping
surement of concentration which does not agree with that
level but known type and composition, for example, n-type
obtained by other techniques.
silicon, can be determined by measuring n and relating this
PR
6.4 GaAs has a sharp reflection minimum due to lattice
to the carrier concentration through an appropriate empirical
−1
reflection (Reststrahlen Band) centered at 302 cm . Therefore
relationship.
measurements of p and n-type GaAs near the lower limit of this
test method should be interpreted carefully so that the Rest-
2 strahlen minium is not mistaken for a plasma resonance
Annual Book of ASTM Standards, Vol 03.06.
Annual Book of ASTM Standards, Vol 10.05. minimum.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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F 398
7. Apparatus 9. Calibration
7.1 Spectrophotometer, Dual-Beam, with either wavelength 9.1 Spectrophotometer:
or a wavenumber presentation, under continuous dry-nitrogen 9.1.1 Refer to the instruction manual for the details of
or dry-air purge, and with the following additional character- operation of the instrument to be used.
istics: 9.1.2 Determine that the wavelength accuracy and repeat-
−1 −1
7.1.1 Wavenumber range from 5000 cm to 25 cm . ability are within the specifications for the instrument in
Wavelength range from 2 to 40 μm. If the range of values is accordance with Practice E 275.
smaller, the range of impurity concentrations covered by the
NOTE 3—It is advised that a service representative of the manufacturer
method is reduced from that stated in 1.2.
be contacted if the accuracy and repeatability determined above are
7.1.2 Provision for up to a ten-times scale expansion of the
outside the manufacturer’s specifications.
reflectance measurement can be necessary for some materials.
9.2 Reflectance Accessory:
7.1.3 Wavelength reproducibility of at least 60.05 μm as
9.2.1 With the accessories to be used for reflectance mea-
determined according to Practice E 275.
surements installed in each beam and with a front surface
−1
7.1.4 Spectral resolution of 2 cm or smaller at 1000
mirror on each reflectance attachment used, displace the scale
−1
cm .
towards zero by adjusting the zero control or some other
7.2 Reflectance Accessory, compatible with the spectropho-
control which does not change the 0 to 100% span. Run a
tometer. This accessory must provide an angle of incidence
double-beam 100% reflectance trace (Fig. 1).
upon the specimen of 30° or less. Additionally, there shall be
9.2.2 The condition of the instrument is not acceptable for
either an identical or symmetric accessory for the reference
this method if this trace varies by more than 8 percentage
beam providing equal path lengths in both beams, or an
points, peak to peak.
attenuator for the reference beam. Whether a reflectance
9.2.3 If the trace varies by more than this amount run a
attachment or an attenuator is used in the reference beam, the
100% trace in double-beam transmission operation.
combination of specimen reflectance attachment and reference
9.2.4 If this trace varies by more than an acceptable value as
beam attachment must provide a 100% trace varying from a
stated by the manufacturer of the spectrometer, the spectrom-
straight line by not more than 8% of a full scale (see 9.2).
eter is not operating properly and must be readjusted.
NOTE 2—While good optical practice would require the use of reflec- 9.2.5 If this trace is within the manufacturer’s specification
tance accessories in each beam so designed and installed as to maintain the
the reflectance attachments are the cause of the error and either
identical path length nature of a dual beam spectrophotometer, the data
they should be carefully aligned or the manufacturer contacted.
from the round robin indicate that the use of an attenuator in the reference
beam does not deteriorate the interlaboratory precision of the measure-
10. Procedure
ment. Therefore the use of a matched pair of reflectance accessories is not
10.1 If the conductivity type of the specimen is unknown
required but is recommended.
determine it at a convenient time before interpretation of the
7.3 Aluminum Mirror, optical quality, scratch-free, front-
measurement, according to Test Methods F 76 or F 42.
surface, for each reflectance attachment to be used.
10.2 Measure the reflectance of the specimen as a function
8. Test Specimens
of wavenumber (Fig. 2, Trace 1). Scan speed must be slow
8.1 The surface of the test specimen must be smooth and enough to allow the instrument to meet the requirements of
highly reflecting, giving the appearance of a mirror, as is 7.1.3 and 7.1.4. If a minimum is not observed, the specimen is
normally used for semiconductor processing. not within the range of applicability of this test method.
8.2 The polishing technique that is used to prepare the 10.3 Expand the reflectance scale if the difference between
surface of the test specimen must minimize subsurface damage the reflectance at the minimum and the greatest reflectance on
(Note 1). either side of the minimum is less than 10 percentage points in
FIG. 1 Displaced 100% Double Beam Reflectance Curve with Front Surface Aluminum Mirrors on the Reflectance
Attachments in Each Beam
...