Mask set mismatch

Claim 1

In a mask set comprised of a plurality of separate masks for producing integrated circuits, where each separate mask contains a plurality of similarly positioned images, a method of minimizing mismatch between the similarly positioned images provided on each mask in the set when the masks are assembled in a set and used to produce the circuits, comprising the steps of; forming a first mask, aligning said first mask to a fixed known standard, determining the coordinates of the centroid of all image fields on said first mask, forming a second mask, aligning said second mask to said fixed known standard, determining the coordinates of the centroid of all fields on said second mask, and marking said second mask with respect to said first mask so that said second mask may be aligned with said first mask to cause the determined centroid of the second mask to overlie the determined centroid of the first mask to minimize the mismatch between the similarly positioned image fields on said first and said second masks and reduce the overall average error of the said similarly positioned image fields to zero.