ASTM F576-01

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.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 576 – 01
Standard Test Method for
Measurement of Insulator Thickness and Refractive Index
1
on Silicon Substrates by Ellipsometry
This standard is issued under the fixed designation F 576; 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
When this test method was developed in the mid-1970’s, manual-null ellipsometers, which are the
basis of this test method, were in routine use. More recently, faster, automated instruments have
replaced manual-null ellipsometers for all common use in the semiconductor industry. There are two
basic types of such automated instruments commonly used: the rotating element null ellipsometer and
the rotating element photometric ellipsometer. For each of these, microprocessors or microcomputers
are used to operate the instrument and to analyze the data. Details of the procedures utilized in these
instruments are usually considered to be proprietary by the instrument manufacturers.
Despite the fact that this test method is not commonly used in its present form, it embodies all the
basic elements of this test method and a simple analysis of data. Thus, it provides useful guidance in
the fundamentals and application of ellipsometry to film thickness measurements. Until a test method,
or test methods, can be developed that cover the newer, automated instruments, this test method
provides the only such information that is available in a standard test procedure. It also contains results
of a test of interlaboratory precision on silicon dioxide films from 20 to 280 nm using manual null
ellipsometers, and of a test of interlaboratory precision of films of 5 to 550 nm using both manual null
ellipsometers as well as automated ellipsometers of both types just mentioned.
Two major changes have occurred since this test method was initially adopted. First, reference
materials certified for the thickness of silicon dioxide layers on silicon are available both from the
National Institute of Standards and Technology and from commercial sources. These can be used to
evaluate the performance of automated ellipsometers. Second, significantly improved materials and
procedures have been developed for storage of reference wafers needed for long term testing of
baseline performance of ellipsometers. It is not uncommon for reference wafers simply to be stored
“clean” with no further wafer-cleaning utilized. If cleaning steps are in fact, utilized, they are not those
described in this test method. The cleaning steps detailed in this test method are retained, however, to
provide background information on procedures used for the first of the interlaboratory tests.
1. Scope 1.4 The precision of this test method is reduced by varia-
tions, over regions smaller than the light-beam spot size, in
1.1 This test method covers the measurement by ellipsom-
substrate flatness, insulator thickness, and index of refraction.
etry of the thickness and refractive index of an insulator grown
1.5 Film thickness measurements determined by ellipsom
or deposited on a silicon substrate.
etry are not unique. When the film thickness is greater than that
1.2 This test method uses monochromatic light.
2 2 1/2
calculated from the expression Nl/[2(n − sin f ) ], where
0
1.3 This test method is nondestructive and may be used to
N is an integer, l the measurement wavelength, n the index of
measure the thickness and refractive index of any film not
refraction, and f the angle of incidence, the thickness value
0
absorbing light at the measurement wavelength on any sub-
determined by this expression must be added to the thickness
strate (1) not transparent to light at the measurement wave-
value determined by ellipsometry to obtain the correct film
length, and (2) of a material for which both the refractive index
thickness. The value of N must be obtained by another
and the absorption coefficient are known at the measurement
procedure.
wavelength.
1.6 Two procedures for computing the results are provided.
If the graphical procedure is used, the measuring wavelength
1
This test method is under the jurisdiction of ASTM Committee F01 on
shall be either 546.1 or 632.8 nm, and the angle of incidence
Electronics and is the direct responsibility of Subcommittee F01.06 on Electrical
shall be 70 6 0.1°.
and Optical Measurements.
Current edition approved June 10, 2001. Published August 2001. Originally
1.7 This test method may be used for referee measurements
published as F 576 – 78. Last previous edition F 576 – 00.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
1

-------
...