Patent ID: 8612903

Claim:
A computer-implemented method for calculating a modification to a reflective photo-mask, comprising: aligning a mask pattern in a first image of the reflective photo-mask and a second image of the reflective photo-mask, wherein the first image and the second image correspond to different types of analysis techniques that measure information associated with at least one of a contour in the mask pattern and a profile of the reflective photo-mask; identifying a group of potential defects in the reflective photo-mask based on the aligned first and second images; and calculating the modification to the reflective photo-mask based on at least a subset of the group of potential defects using an inverse optical calculation to correct an impact of at least the subset of the defects in a photo-lithographic process, wherein, during the inverse optical calculation, a cost function at an image plane in a model of the photolithographic process is used to determine the modification to the reflective photo-mask at an object plane in the model of the photolithographic process, wherein the cost function corresponds to a difference between a reference pattern associated with a target mask pattern and a calculated pattern associated with a modified reflective photo-mask, and wherein the modified reflective photo-mask includes the modification to the reflective photo-mask determined in a previous iteration during the inverse optical calculation.