Patent ID: 9390494
Filing Date: 2016-07-12
CPC Classification: G01N,G06T

Claim Text:
1. A method of inspecting a photolithographic reticle, the method comprising: with an optical inspection tool, obtaining a plurality of patch images of a plurality of patches of a plurality of dies of the reticle, wherein the dies are designed to be identical, and wherein the patch images are obtained so that each patch image is positioned relative to a same reference position within its respective die as another die-equivalent one of the patch images in each of a plurality of other ones of the dies; for each patch image, determining an integrated value for an image characteristic of a plurality of sub-portions of such patch image; for each patch image, determining a reference value based on the integrated values of the patch image's corresponding die-equivalent patch images; for each patch image, determining a difference between that patch image's integrated value and an average or median value of the integrated values of the patch image's die-equivalent patch images whereby such difference indicates a difference between a pattern characteristic of any patch and an average or median pattern characteristic of its die-equivalent patches; generating a delta map based on the determined difference for each patch image; and detecting defects on the reticle based on the delta map.