Patent ID: 7796238

Claim:
A wafer pre-alignment method comprising: transferring wafers from a standby location in an exposure unit to an alignment apparatus, detecting the relative angular positions of the wafers at the alignment apparatus, respectively, controlling the alignment apparatus to adjust the relative angular positions of each of the wafers by respective amounts necessary to set each of the wafers in the same relative angular position, whereby misalignment of the wafers with respect to a reference position is first compensated for, returning each of the wafers to the standby location, and calculating an inherent error value for the exposure unit based on the relative angular positions of the wafers detected when the wafers are at the alignment apparatus; and subsequently transferring the wafers in the exposure unit from the standby location back to the alignment apparatus, and controlling the alignment apparatus to adjust the orientation of the wafers each by an amount corresponding to the inherent error value calculated for the exposure unit, whereby misalignment of the wafers with respect to the reference position is secondly compensated for.