Patent ID: 7691542

Claim:
A method for evaluating lithography process comprising: (a) coating a first resist on a test wafer; (b) projecting, onto an identical exposure field on the first resist, images of a mask, the mask including: a grating pattern; and a test pattern having an opening; wherein a first image of the grating pattern is a first line and space pattern having a plurality of lines between spaces, and an image of the opening in the projected image of the test pattern overlaps with a part of the first line and space pattern so that the image of the opening is surrounded by the first line and space pattern; (c) measuring first critical dimensions of the first line and space pattern by measuring a first line width of lines of the first line and space pattern at a plurality of first positions around the image of the opening, the first positions being assigned from an edge of the image of the opening to a surrounding area of the image of the opening in the exposure field and having different distances from the edge; (d) coating a second resist on a reference wafer; (e) protecting, onto the second resist, a second image of the grating pattern of the mask, wherein the second image of the grating pattern is a second line and space pattern having a plurality of lines between spaces; (f) measuring second critical dimensions of the second line and space pattern by measuring a second line width of lines of the second line and space pattern at a plurality of second positions, the second positions corresponding to the first positions; and (g) estimating an influence of a pattern density of the mask upon critical dimension variations by comparing the first critical dimensions and the second critical dimensions.