ASTM F95-89(2000)

Standard Test Method for Thickness of Lightly Doped Silicon Epitaxial Layers on Heavily Doped Silicon Substrates Using an Infrared Dispersive Spectrophotometer (Withdrawn 2003)

SCOPE
This standard was transferred to SEMI (www.semi.org) May 2003
1.1 This test method provides a technique for the measurement of the thickness of epitaxial layers of silicon deposited on silicon substrates. A dispersive infrared spectrophotometer is used. For this measurement, the resistivity of the substrate must be less than 0.02[omega] cm at 23oC and the resistivity of the layer must be greater than 0.1[omega] cm at 23oC.
1.2 This technique is capable of measuring the thickness of both n- and p-type layers greater than 2 µm thick. With reduced precision, the technique may also be applied to both n- and p-type layers from 0.5 to 2 µm thick.
1.3 This test method is suitable for referee measurements.
1.4This 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.

General Information

• Status: Withdrawn
• Publication Date: 31-Dec-1999
• Withdrawal Date: 09-May-2003
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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.
Designation: F 95 – 89 (Reapproved 2000)
Standard Test Method for
Thickness of Lightly Doped Silicon Epitaxial Layers on
Heavily Doped Silicon Substrates Using an Infrared
Dispersive Spectrophotometer
ThisstandardisissuedunderthefixeddesignationF95;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
In editions of this test method published through 1987, the title and scope of the method required
that the epitaxial layer and substrate be of the same conductivity type.This requirement was dropped,
allowing the epitaxial layer and substrate to be of opposite conductivity type in the revision first
published in 1988, subject to the continuing requirements of minimum allowed resistivity of the
epitaxial layer and maximum allowed resistivity of the substrate. This same revision changed
specifications on dispersive instruments from wavelength values to wave number values, where
appropriate. A brief description of the theory of this test method is given in Appendix X1.
Automated test systems, utilizing Fourier-Transform Infrared Spectrophotometry (FT-IR) are
widely used for epitaxial layer thickness measurements. Because such instruments are normally
supplied with proprietary software for measurement analysis, detailed procedures for the use of such
instruments are not included in this test method. However, for information purposes, estimates of
single instrument repeatability and multiinstrument reproducibility, based on a 1986/1987 multilabo-
ratory comparison of FT-IR instrument measurements are given in Note 6 and Appendix X2.
Automated test systems, utilizing Fourier-Transform Infrared Spectrophotometry (FT-IR) are
widely used for epitaxial layer thickness. Because such instruments are normally supplied with
proprietary software, detailed procedures for the use of such instruments are not included in this test
method.
1. Scope 1.3 This test method is suitable for referee measurements.
1.4 This standard does not purport to address all of the
1.1 This test method provides a technique for the measure-
safety concerns, if any, associated with its use. It is the
mentofthethicknessofepitaxiallayersofsilicondepositedon
responsibility of the user of this standard to establish appro-
silicon substrates. A dispersive infrared spectrophotometer is
priate safety and health practices and determine the applica-
used.Forthismeasurement,theresistivityofthesubstratemust
bility of regulatory limitations prior to use.
be less than 0.02 V·cm at 23°C and the resistivity of the layer
must be greater than 0.1 V·cm at 23°C.
2. Referenced Documents
1.2 This technique is capable of measuring the thickness of
2.1 ASTM Standards:
both n-and p-typelayersgreaterthan2µmthick.Withreduced
E 177 Practice for Use of the Terms Precision and Bias in
precision, the technique may also be applied to both n- and
ASTM Test Methods
p-type layers from 0.5 to 2 µm thick.
E 932 Practice for Describing and Measuring Performance
of Dispersive Infrared Spectrophotometers
F84 Test Method for Measuring Resistivity of Silicon
This test method is under the jurisdiction of ASTM Committee F01 on
Slices with an In-Line Four-Point Probe
Electronics and is the direct responsibility of Subcommittee F01.06 on Silicon
Materials and Process Control.
3. Terminology
Current edition approved Aug. 25, 1989. Published October 1989. Originally
published as F95–68T. Last previous edition F95–88a.
3.1 Definitions:
DIN 50437 is an equivalent method. It is the responsibility of DIN Committee
NMP221,withwhichCommitteeF-1maintainsclosetechnicalliaison.DIN50437.
Testing of Inorganic Semiconductor Materials: Measurement of the Thickness of
Silicon Epitaxial Layers by the Infrared Interference Method, is available from Annual Book of ASTM Standards, Vol 14.02.
BeuthVerlagGmbHBurggrafenstrasse4-10,D-1000Berlin30,FederalRepublicof Annual Book of ASTM Standards, Vol 03.06.
Germany and Vol 10.05. Annual Book of ASTM Standards, Vol 10.05.
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.
F 95 – 89 (2000)
3.1.1 epitaxial layer—in semiconductor technology, a layer 5.2 Specimen Holder— The specimen holder shall be so
of semiconductor material having the same crystalline spacing constructed that no damage can be inflicted by the holder on
as the host substrate on which it is grown. the epitaxial layer.
3.1.2 index of refraction—the relative index of refraction is 5.3 Masking Aperture— The size of the masking aperture
defined by Snell’s law as the ratio of the sine of the angle of shallbesuchastorestricttheilluminatedareaonthespecimen
incidence to the sine of the angle of refraction. The angles are surface to a value sufficiently small to eliminate the effect of
measured between the surface normal and the infrared beam. thickness fluctuations, without impairing detection of the
The value of this index for the wavelength range from 6 to 40 reflected light.The masking aperture shall be constructed from
µm is 3.42 relative to air for silicon having resistivity greater a nonreflecting material such as matte-surface graphite.
than 0.1 V·cm.
6. Test Specimen
3.1.3 interface—theboundarybetweenthesubstrateandthe
epitaxial layer as determined by this technique. 6.1 The specimen surface shall be highly reflective, free
3.1.4 substrate—in semiconductor technology, a wafer that from large-area imperfections, and free of passivating layers
is the basis for subsequent processing operations in the except native oxides. The specimen surface may be cleaned
fabrication of semiconductor devices or circuits. prior to measurement by any technique which does not affect
3.1.4.1 Discussion—The devices or circuits may be fabri-
the specimen polish or the layer thickness.
cateddirectlyinthesubstrateorinafilmofthesameoranother
7. Preparation ofApparatus
material grown or deposited on the substrate.
7.1 Establish the maximum allowable scan speed as fol-
4. Summary of Test Method
lows:
7.1.1 Choose a specimen with a substrate resistivity be-
4.1 The reflectance of the specimen is measured as a
tween 0.008 and 0.02 V·cm, (see Scope) and an epitaxial layer
function of wave number using an infrared spectrophotometer.
ofsuchthicknessthatanobservableminimumoccursatawave
The reflectance spectrum of a suitable specimen exhibits
−1
number less than 400 cm .
successive maxima and minima characteristic of optical inter-
7.1.2 Choose a suitable masking aperture.
ference phenomena. The thickness of the epitaxially deposited
7.1.3 Place the specimen on the instrument and record the
layer is calculated using the wave numbers of the extrema in
−1
spectrumofaminimumwavenumberlessthan400cm using
the reflectance spectrum, the optical constants of the layer and
the slowest scan speed available.
the substrate, and the angle of incidence of the infrared beam
7.1.4 Record the position of the minimum.
upon the specimen.
7.1.5 Increase the scan speed in steps and record the
position of the minimum for each scan speed.
5. Apparatus
7.1.6 Allowablescanspeedsarethosewhichshowashiftof
5.1 Double-Beam Infrared Spectrophotometer—This appa-
−1
the minimum of less than 61cm relative to the position of
ratus shall utilize monochromatic infrared light of known and
the minimum as determined at the slowest scan speed.
variable wave numbers. This light shall be reflected from the
specimen and the reflectivity shall be recorded as a function of
8. Procedure
wave number. It is essential that the wave numbers indicated
8.1 Handle the specimen carefully to avoid surface damage
by the apparatus be carefully calibrated. Calibration accuracy
to the thin epitaxial layer.
shall be determined in accordance with Practice E932E 932,
8.2 Placethespecimenovertheaperturemasktoexposethe
−1
using polystyrene lines at 1601.6 and 648.9 cm . The calibra-
desired location to the beam.
tion accuracy shall be 0.05 µm. The useful range of wave
8.3 Obtain a reflection spectrum similar to that shown in
−1
number is 1670 to 250 cm . The precision and thickness
Fig. 1. Do not attempt a calculation of layer thickness if the
capabilities stated in Section 11 were established using data in
peak amplitude to noise amplitude ratio is less than five.
−1
the range 900 to 300 cm . In general, thinner specimens
require a broader wavelength range than thicker ones. NOTE 1—The interference pattern may be obscured or illegible if the
FIG. 1 Typical Reflection Spectrum for n-Type Specimen
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.
F 95 – 89 (2000)
TABLE 1 Phase (Shifts (f/2p)for n -Type Silicon
Wave- Resistivity, V·cm
length,
0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010 0.012 0.014 0.016 0.018 0.20
µm
2 0.033 0.029 0.028 0.027 0.027 0.026 0.025 0.024 0.023 0.022 0.020 0.019 0.017 0.016 0.021
4 0.061 0.050 0.047 0.046 0.045 0.043 0.041 0.039 0.038 0.036 0.034 0.031 0.029 0.027 0.025
6 0.105 0.072 0.064 0.062 0.060 0.057 0.055 0.052 0.050 0.048 0.044 0.042 0.039 0.036 0.033
8 0.182 0.099 0.083 0.078 0.075 0.071 0.067 0.064 0.016 0.059 0.054 0.051 0.047 0.043 0.040
10 0.247 0.137 0.105 0.095 0.090 0.084 0.079 0.075 0.071 0.069 0.063 0.059 0.055 0.051 0.047
12 0.289 0.183 0.132 0.115 0.106 0.098 0.091 0.084 0.081 0.078 0.072 0.067 0.062 0.057 0.053
14 0.318 0.225 0.164 0.137 0.124 0.113 0.104 0.097 0.092 0.087 0.080 0.074 0.069 0.064 0.059
16 0.339 0.258 0.197 0.163 0.144 0.129 0.117 0.109 0.102 0.097 0.088 0.082 0.075 0.070 0.065
18 0.355 0.283 0.226 0.189 0.166 0.146 0.131 0.121 0.113 0.107 0.096 0.089 0.082 0.076 0.070
20 0.368 0.303 0.251 0.214 0.188 0.165 0.147 0.134 0.124 0.117 0.105 0.096 0.088 0.081 0.075
22 0.378 0.319 0.272 0.236 0.209 0.183 0.163 0.148 0.136 0.127 0.113 0.104 0.095 0.087 0.081
24 0.387 0.333 0.289 0.255 0.229 0.202 0.179 0.162 0.148 0.138 0.122 0.111 0.101 0.093 0.086
26 0.394 0.344 0.303 0.272 0.246 0.219 0.196 0.177 0.161 0.150 0.131 0.119 0.108 0.099 0.091
28 0.401 0.353 0.316 0.286 0.261 0.235 0.211 0.191 0.175 0.161 0.141 0.127 0.115 0.104 0.096
30 0.406 0.362 0.326 0.298 0.275 0.250 0.226 0.206 0.188 0.173 0.150 0.135 0.121 0.110 0.101
32 0.411 0.369 0.336 0.309 0.287 0.263 0.240 0.219 0.210 0.185 0.160 0.143 0.128 0.116 0.106
34 0.415 0.375 0.344 0.319 0.297 0.274 0.252 0.232 0.213 0.197 0.170 0.151 0.135 0.122 0.112
36 0.419 0.381 0.351 0.327 0.307 0.285 0.263 0.243 0.225 0.209 0.180 0.160 0.143 0.129 0.117
38 0.422 0.386 0.357 0.335 0.315 0.294 0.273 0.254 0.236 0.220 0.191 0.167 0.150 0.135 0.123
40 0.425 0.391 0.363 0.341 0.323 0.302 0.283 0.264 0.246 0.230 0.200 0.178 0.158 0.141 0.128
thickness of the epitaxial layer varies by more than 4% over the masking
one order, assign the orders to the remaining extrema in
aperture, or if the interface impurity concentration profile does not
descending order with increasing wavelength as shown in Fig.
approximate a step function.
1.
8.4 Determine the wave number of each extremum in the
9.2 Calculate the thickness using the following equation:
reflectionspectrumbyaveragingtheinterceptsofthereflection
2 2 1/2
T 5[P 21/2 1 ~f /2p!#·l /2~n 2sin u! (2)
n n 2n n 1
spectrum and a horizontal line 3% of full scale below a
maximum or above a minimum. This procedure reduces the
where:
ambiguity encountered when the extrema are broad.
T = epitaxial layer thickness,
n
n = indexofrefractionoftheepitaxiallayer(n =3.42for
1 1
NOTE 2—A more correct procedure for locating the position of the
silicon),
extrema on layers less than 2 µm thick is to draw the tangent envelops to
u = angle of incidence of the beam upon the epitaxial
the spectrum and determine the intersection of the envelopes with the
layer, and
interference spectrum. However, this procedure is apparently more
difficulttoperformsinceitsuseinaround-robintest(see11.3)resultedin
the other symbols have the same meaning they had in Eq 1.
reduced rather than improved precision.
Use the same units for the thickness as for the wavelength.
Calculate T for all of the observed maxima and minima and
8.5 Measure the resistivity of the substrate in the area of the
n
thickness measurement on the side opposite the epitaxial layer calculate the average value of T.
using the four-probe method of Test Method F84F84.
NOTE 3—When several extrema are available, somewhat better preci-
sion than that reported in Section 11 will result if the longer wavelength
9. Calculation
points are excluded from the calculation.
9.1 Determine the orders for the maxima and minima
9.3 Sample Calculation—Typical data and a calculation of
observed using the following equation:
epitaxial layer thickness for an n-type specimen, using the
P 5 ml /~l 2l ! 11/2 2 ~f l 2f l !/2p~l 2l ! (1)
2 1 1 2 2 1 22 2 1 2 reflection spectrum shown in Fig. 1, are as follows:
9.3.1 The measured value of substrate resistivity was 0.014
where:
V/cm.
P = order of the extremum associated with l ,
2 2
9.3.2 Determine wavelength of first and last extrema; l
l = 10000/y ,
1 1
1=31.70 µm and l =15.28 µm.
l = 10000/y ,
2 2
m = differenceintheordersoftheextremaconsidered,and 9.3.3 Read appropriate phase shifts from Table 1: f /
2p=0.142 and f /2p=0.079.
f and f are the phase shifts suffered by the ray reflected
21 22
at the interface for l and l respectively. 9.3.4 Find from Fig. 1 the difference in the orders of the
1 2
9.1.1 Obtain the phase shifts f and f from Table 1 or extrema considered: m =3.5.
21 22
Table 2 . Round off the calculated order, P , to an integer for
9.3.5 Substitute in Eq 1 and solve for P :
amaximumandahalfintegerforaminimum.Aftercalculating
P 53.5 ~31.70!/~31.70 215.28! 11/2 2[31.70 ~0.142!
215.28 ~0.079!#/~31.70 215.28!
56.80 10.50 20.20 57.10 '7
Schumann, P. A., “The Infrared Interference Method of Measuring Epitaxial
Layer Thickness,’’ Journal Electrochemical Society, Vol 116, 1969, p. 410. 9.3.6 Substitute in Eq 2 and solve for T :
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.
F 95 – 89 (2000)
TABLE 2 Phase Shifts (f/2p)for p -Type Silicon
Wave- Resistivity, V·cm
length,
0.001 0.0015 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009
...