This test method covers a noncontacting, nondestructive procedure to
determine the warp of clean,
dry semiconductor wafers.
The test method is applicable to wafers 50 mm or larger in diameter,
and 100 µm (0.004 in.)
approximately and larger in thickness, independent of thickness
variation and surface finish, and
of gravitationally-induced wafer distortion.
This test method is not intended to measure the flatness of either
exposed silicon surface. Warp is
a measure of the distortion of the median surface of the wafer.
This test method measures warp of a wafer corrected for all mechanical
forces applied during the
test. Therefore, the procedure described gives the unconstrained value
of warp. This test method
includes a means of canceling gravity-induced deflection which could
otherwise alter the shape of
the wafer. The resulting parameter is described by Warp(2) in Appendix
X2 Shape Decision Tree in
SEMI Specification M 1. (See Annex A1.)
NOTE 1 - Test Method F 657 measures median surface warp using a
three-point back-surface reference
plane. The back-surface reference results in thickness variation being
included in the recorded
warp value. The use (in this test method) of a median surface
reference plane eliminates this
effect. The use (in this test method) of a least-squares fit reference
plane reduces the
variability introduced in three-point plane calculations by choice of
reference point location. The
use (in this test method) of special calibration or compensating
techniques minimizes the effects
of gravity-induced distortion of the wafer.
The values stated in SI units are to be regarded separately as the
standard. The values given in
parentheses are for information only.
This 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.