ASTM F1535-00

Standard Test Method for Carrier Recombination Lifetime in Silicon Wafers by Noncontact Measurement of Photoconductivity Decay by Microwave Reflectance (Withdrawn 2003)

SCOPE
This standard was transferred to SEMI (www.semi.org) May 2003
1.1 This test method covers the measurement of carrier lifetime appropriate to carrier recombination processes in homogeneously doped, polished, - or -type silicon wafers with room-temperature resistivity greater than about 0.05 [omega][dot]cm. This test method may also be applied to the measurement of carrier recombination lifetime in as-cut, lapped, or etched wafers provided that the sensitivity of the conductivity detection system is adequate.
1.2 In this test method, the decay of the wafer conductivity following generation of excess carriers with a light pulse is determined by monitoring the microwave reflectivity of the wafer. Since no contact is made to the specimen, this test method is nondestructive. If wafer cleanness is maintained, wafers may be further processed following testing by this test method.
1.3 Depending on the level of photoexcitation, the carrier recombination lifetime determined by this test method may be the minority-carrier lifetime (low injection level) or a mixture of minority- and majority-carrier lifetimes (intermediate and high injection levels). In the latter case, the minority and majority carrier lifetimes may be separated under some conditions if a single recombination center that follows the Shockley-Read-Hall model is assumed (see Appendix X1).
1.4 This test method is appropriate for the measurement of carrier recombination lifetimes in the range from 0.25 [mu]s to >1 ms. The shortest measurable lifetime values are governed by the turn-off characteristics of the light source and by the sampling frequency of the decay signal analyzer while the longest values are determined by the geometry of the test specimen and the degree of passivation of the wafer surface. With suitable passivation procedures, such as thermal oxidation or immersion in a suitable solution, lifetimes as long as tens of milliseconds can be determined in polished wafers with thickness as specified in SEMI M1.  Note 1-Carrier recombination lifetime of large bulk specimens can be determined by Method A or B of Test Methods F28. These test methods, which are also based on measurement of photoconductivity decay (PCD), require electrical contacts to the specimen. In addition, they assume large surface recombination on all surfaces and so the upper limit of measurable lifetime is governed by the size of the test specimen. Method B of Test Methods F28 stipulates that the test be carried out under conditions of low injection to ensure that the minority-carrier lifetime is determined. Minority-carrier lifetime can also be deduced from the carrier diffusion length as measured by the surface photovoltage (SPV) method in accordance with Method A or B of Test Methods F391. When carried out under low injection conditions, both the SPV method and the PCD method should yield the same values of minority-carrier lifetime (1)  under certain conditions. First, it is required that carrier trapping not occur. Second, correct values of absorption coefficient and minority-carrier mobility must be used in analyzing the SPV measurements. Third, surface recombination effects must be eliminated (as in the present test method) or properly accounted for (as in Test Methods F28) in carrying out the PCD measurements. The generation lifetime, which is another transient characteristic of semiconductor materials, is typically orders of magnitude larger than the recombination lifetime. Although Test Method F1388 covers the measurement of the generation lifetime in silicon wafers, the recombination lifetime can also be deduced from capacitance-time measurements made at temperatures above room temperature ([>=]70°C) using the same MOS capacitor structure (2).
1.5 Interpretation of measurements to identify the cause or nature of impurity centers is beyond the scope of this test method. However, some aspects of deriving this information from carrier recombination lifetime m...

General Information

• Status: Withdrawn
• Publication Date: 09-Jun-2000
• Withdrawal Date: 12-Aug-2003
• ICS: 29.045 - Semiconducting materials
• Technical Committee: F01 - Electronics

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 1535 – 00
Standard Test Method for
Carrier Recombination Lifetime in Silicon Wafers by
Noncontact Measurement of Photoconductivity Decay by
1
Microwave Reflectance
This standard is issued under the fixed designation F 1535; 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.
determined by Method A or B of Test Methods F 28. These test methods,
1. Scope
which are also based on measurement of photoconductivity decay (PCD),
1.1 This test method covers the measurement of carrier
require electrical contacts to the specimen. In addition, they assume large
lifetime appropriate to carrier recombination processes in
surface recombination on all surfaces and so the upper limit of measurable
homogeneously doped, polished, n-or p-type silicon wafers
lifetime is governed by the size of the test specimen. Method B of Test
with room-temperature resistivity greater than about 0.05 Methods F 28 stipulates that the test be carried out under conditions of low
injection to ensure that the minority-carrier lifetime is determined.
V·cm. This test method may also be applied to the measure-
Minority-carrier lifetime can also be deduced from the carrier diffusion
ment of carrier recombination lifetime in as-cut, lapped, or
length as measured by the surface photovoltage (SPV) method in
etched wafers provided that the sensitivity of the conductivity
accordance with Method A or B of Test Methods F 391. When carried out
detection system is adequate.
under low injection conditions, both the SPV method and the PCD method
1.2 In this test method, the decay of the wafer conductivity 2
should yield the same values of minority-carrier lifetime (1) under certain
following generation of excess carriers with a light pulse is
conditions. First, it is required that carrier trapping not occur. Second,
determined by monitoring the microwave reflectivity of the correct values of absorption coefficient and minority-carrier mobility must
be used in analyzing the SPV measurements. Third, surface recombination
wafer. Since no contact is made to the specimen, this test
effects must be eliminated (as in the present test method) or properly
method is nondestructive. If wafer cleanness is maintained,
accounted for (as in Test Methods F 28) in carrying out the PCD
wafers may be further processed following testing by this test
measurements. The generation lifetime, which is another transient char-
method.
acteristic of semiconductor materials, is typically orders of magnitude
1.3 Depending on the level of photoexcitation, the carrier
larger than the recombination lifetime. Although Test Method F 1388
recombination lifetime determined by this test method may be
covers the measurement of the generation lifetime in silicon wafers, the
recombination lifetime can also be deduced from capacitance-time mea-
the minority-carrier lifetime (low injection level) or a mixture
surements made at temperatures above room temperature ($70°C) using
of minority- and majority-carrier lifetimes (intermediate and
the same MOS capacitor structure (2).
high injection levels). In the latter case, the minority and
majority carrier lifetimes may be separated under some condi- 1.5 Interpretation of measurements to identify the cause or
nature of impurity centers is beyond the scope of this test
tions if a single recombination center that follows the
Shockley-Read-Hall model is assumed (see Appendix X1). method. However, some aspects of deriving this information
from carrier recombination lifetime measurements alone is
1.4 This test method is appropriate for the measurement of
discussed in the appendices. Use of “injection level spectros-
carrier recombination lifetimes in the range from 0.25 μs to >1
ms. The shortest measurable lifetime values are governed by copy” (3) are discussed in Appendix X1 and use of the
temperature dependence of the carrier recombination lifetime
the turn-off characteristics of the light source and by the
sampling frequency of the decay signal analyzer while the as determined with low-injection level (4) is discussed in
Appendix X2. The identity and density of impurity centers
longest values are determined by the geometry of the test
specimen and the degree of passivation of the wafer surface. found to be present in the wafer by means of recombination
lifetime measurements may usually be determined more reli-
With suitable passivation procedures, such as thermal oxida-
tion or immersion in a suitable solution, lifetimes as long as ably from deep-level transient spectroscopy (DLTS) measure-
ments made in accordance with Test Method F 978
...