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.