Patent ID: 7804993

Claim:
A method for inspecting a wafer including a multiplicity of dies using an inspection apparatus, the method comprising: aligning a plurality of images of purportedly identical portions of the wafer thereby to provide a plurality of mutually aligned images, said aligning including applying sub-pixel corrections to said images using a same-smear re-sampling filter which, for each respective one of the plurality of images, determines whether a respective image portion's misalignment (dx,dy) relative to a selected alignment marker is 0.5 pixel, and, if so, aligns the plurality of images with a (0.5,0.5) filter, and otherwise, aligns the plurality of images with a filter of order n>2 having a shift (dx,dy) and a frequency response that approximates a frequency response of said (0.5,0.5) filter, said plurality of mutually aligned images thereby having an essentially identical amount of smear.