Patent ID: 7241541
Filing Date: 2007-07-10
Classification: G03F

Abstract:
1. A method for determining mask to mask error for improving the overlay of a second layer pattern on a first layer pattern formed in a substrate, said first layer pattern is formed by exposing a first photoresist layer through a first layer mask and transferring the first layer pattern into a substrate and the second layer pattern is formed by exposing a second photoresist layer with a second layer mask, comprising: (a) providing a first layer mask comprised of an inner pattern area, an outer region, and a plurality of first reference marks formed within the inner pattern area and on the outer region, said first reference marks each have a center point with (x,y) coordinates; (b) providing a second layer mask comprised of an inner pattern area, an outer region, and a plurality of second reference marks each formed within the inner pattern area and on the outer region wherein each second reference mark is matched with a first reference mark and has a center point with the same (x,y) coordinates as a matching first reference mark on the first layer mask; (c) measuring the (x,y) coordinates for the center points of the first reference marks and second reference marks and determining the offset values in terms of x and y deviations for each matched pair of first and second reference marks; and (d) inputting the offset values into an error table and applying a correction algorithm to the data in the error table which calculates adjustments in exposure tool settings that are subsequently used to expose a second layer pattern with the second layer mask on a first layer pattern in a substrate that has been formed with the first layer mask.