Patent ID: 7975244

Claim:
A method of designing a mask including using pixel-based model for simulating a lithographic process, the method comprising the steps of: providing a minimum step size for modifying mask shapes; selecting a pixel grid size larger than said minimum step size; providing a test pattern comprising a plurality of rows of features, wherein each row of features is separated from an adjacent row of features along a y-direction orthogonal to an x-direction by a y-separation greater than or equal to a region of influence, and wherein each row of said plurality of rows comprises the same sequence of a plurality of features, wherein said features each have a feature width along said x-direction, and each of said feature widths within each row differ from every other feature width within said row by a multiple of said minimum step size, and wherein a starting location of each row is offset along the x-direction from the starting location of each of other rows of said plurality of rows by an x-separation that is different for each pair of rows and said x-separation ranges from said minimum step size to at least said pixel grid size by an integer multiple of said minimum step size; determining, by a processor, images of said test pattern using said pixel grid size; determining a numerical error metric of a comparison between said image of a reference row with said image of each other row in said test pattern; and designing said mask using said pixel grid size if said numerical error metric meets a predetermined criterion.