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SEMI MF533 Document Information:
Title
TEST METHODS FOR THICKNESS AND THICKNESS VARIATION OF SILICON WAFERS
Semiconductor Equipment and Materials International
Publication Date:
Nov 1, 2009
Scope:
These test methods cover measurement of the thickness of silicon
wafers, polished or unpolished, and estimation of the variation in
thickness across the wafer for both flatted and notched wafers. For
flatted wafers of 200 mm diameter or less, a five-point pattern
offset from the bisector of the primary flat is used. For notched
wafers of 200 mm diameter or more, either a symmetrical five-point
or nine-point pattern is used.
NOTE 1: DIN 50441/1 is an equivalent method.
These test methods are intended primarily for use with wafers
that meet the dimension and tolerance requirements of SEMI M1.
However, they can be applied to circular silicon, wafers or
substrates of any diameter and thickness that can be handled
without breaking.
These test methods are suitable for both contact and contactless
gaging equipment. Precision statements have been established for
each in the case of the five-point method applied to flatted
wafers.
The values stated in inch-pound units are to be regarded as the
standard for measurements on wafers of 3 inch diameter or less
while the metric units are to be regarded as the standard for
measurements on wafers of 100 mm diameter or more.
NOTICE: This standard does not purport to
address safety issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety and health practices and determine the
applicability of regulatory or other limitations prior to use.
Purpose
Wafer thickness and thickness variations must be controlled to
suit the requirements of fixtures and equipment used in
microelectronic processing. Estimates of these parameters, based on
a representative sample from a given lot of wafers, aids in
determining whether or not wafers from that lot are acceptable for
the intended processing steps.
Wafers that are too thin may break during normal processing
operations. Wafers that are too thick may cause mechanical jamming.
Wafers with thickness outside the desired tolerance may not have
appropriate thermal mass or electrical resistance for certain
processing steps.
Excessive thickness variations may cause problems with
mechanical handling of the wafers during processing. In addition,
such variations may cause deviations from surface flatness that
adversely affect photolithographic processes. The effect of
thickness variations on photolithographic processes depends on the
line width and registration requirements of individual circuit
designs, as well as on the specific optical and mechanical design
of the photolithographic processing equipment being used.
These test methods are intended for use for materials acceptance
and process control purposes. The test methods may be applied at
any point during the processing of unpolished wafers into polished
wafers or substrates.
When the test method for flatted wafers was developed in the
1970s, non-contact thickness gages employing manual wafer
positioning, which are the basis of this test method, were in
routine use. More recently, faster, automated instruments have
replaced these manual gages for most common uses in the
semiconductor industry. In these automatic systems, microprocessors
or microcomputers are used to control wafer positioning, operate
the instrument and to analyze the data (see SEMI MF1530).
Despite the fact that these test methods are not commonly used
in its present form, they embody all the basic elements of the
measurement method and a simple analysis of data. Thus, this
standard provides useful guidance in the fundamentals and
application of differential non-contact wafer thickness
measurements. They are also suitable for use with very large
diameter wafers before the automatic systems become available.
Keywords:
- semiconductor
- silicon
- thickness
- thickness variation
- total thickness variation
- wafer
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