Patent ID: 7793253

Claim:
A computer-implemented method for determining a mask pattern to be used on a photo-mask in a photolithographic process, wherein the photo-mask has a plurality of distinct types of regions having distinct optical properties, comprising: providing a target pattern, wherein the target pattern includes at least one continuous feature having two portions that intersect each other, the two portions having, respectively, a first symmetry axis and a second symmetry axis; and determining, using at least one processor in the computer, the mask pattern that includes a plurality of distinct types of regions corresponding to the distinct types of regions of the photo-mask, wherein the mask pattern includes a first feature and a second feature corresponding to at least the one continuous feature, the first feature having a third symmetry axis which is substantially parallel to the first symmetry axis, the second feature having a fourth symmetry axis which is substantially parallel to the second symmetry axis, wherein the first feature and the second feature are separated by a gap having a length which overlaps at least one of the two portions of at least the one continuous feature proximate to the intersection of the two portions, and wherein the first feature and the second feature substantially overlap at least the one continuous feature, wherein the determining includes calculating a gradient of a function, wherein the function depends on an initial mask pattern and the estimate of a wafer pattern to be printed using the photo-mask in the photo-lithographic process, and wherein the gradient is calculated in accordance with a formula obtained by taking a derivative of the function.