US Patent 10957035 Defect classification by fitting optical signals to a point-spread function

A semiconductor die is inspected using an optical microscope to generate a test image of the semiconductor die. A difference image between the test image of the semiconductor die and a reference image is derived. For each defect of a plurality of defects for the semiconductor die, a point-spread function is fit to the defect as indicated in the difference image and one or more dimensions of the fitted point-spread function are determined. Potential defects of interest in the plurality of defects are distinguished from nuisance defects, based at least in part on the one or more dimensions of the fitted point-spread function for respective defects of the plurality of defects.