Abstract
Accurate flatness measurement of silicon wafers is affected greatly by the
gravity-induced deflection (GID) of the wafers, especially for large and
thin wafers. The three-point-support method is a preferred method for the
measurement, in which the GID uniquely determined by the positions of the
supports could be calculated and subtracted. The accurate calculation of
GID is affected by the initial stress of the wafer and the positioning
errors of the supports. In this paper, a finite element model (FEM)
including the effect of initial stress was developed to calculate GID. The
influence of the initial stress of the wafer on GID calculation was
investigated and verified by experiment. A systematic study of the effects
of positioning errors of the support ball and the wafer on GID calculation
was conducted. The results showed that the effect of the initial stress
could not be neglected for ground wafers. The wafer positioning error and
the circumferential error of the support were the most influential factors
while the effect of the vertical positioning error was negligible in GID
calculation.
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