Patent Document ID: 4672676
Application ID: 06684632
Patent Status: 1

Claim One:
1. A method for automatically aligning an object with respect to a reference, said object having a pair of alignment marks each having a given area, said reference being comprised of two inspection windows whose centers are located a distance d from each other along an axis of reference and whose center comprises a center of reference, said method being characterized in that it comprises the steps of: placing said object on an alignment platen; positioning said object so that each alignment mark (I.sub.MIR, I'.sub.MIR) thereon appears entirely within one said inspection window; generating at the center of each inspection window a virtual image (I.sub.REF) of an alignment mark, said virtual image having the same dimensions as an alignment mark (I.sub.MIR, I'.sub.MIR), said virtual image being superimposed over the alignment mark in each said inspection window; determining exposed portion which comprises the portion of the alignment mark (S.sub.i.sup.+, S.sub.i.sup.+ '), where i is 1,2,3 and 4, in each quadrant of each inspection window which does not have said virtual image superimposed over it and determining masked portions comprising the portion of the virtual image (S.sub.I.sup.-, S.sub.i.sup.- ') in each quadrant of each inspection window which does not superimpose the alignment mark; calculating, using computation means responsive to said exposed portions and said masked portions, the translational (.DELTA.X and .DELTA.Y) and rotational (.DELTA..theta.) correction needed to position said object in alignment with said virtual image and causing said alignment platen to be translationally and rotationally adjusted to thereby position said object in alignment with said virtual image.