Automatic photomask and reticle inspection method and apparatus including improved defect detector and alignment sub-systems

摘要

A photomask and reticle inspection method and apparatus wherein a selected surface area of an object is inspected and a first stream of data having signal values representing the image content of each pixel thereof is generated, a second stream of data having signal values representing the intended image content of each pixel of the first stream of data is generated, corresponding portions of the first and second streams of data are stored in memory, any misalignment between the stored portions of the first and second streams of data is detected, the misaligned first and second portions of data are then aligned using shifts of an integral number of pixels and/or subpixel interpolation to correct the detected misalignment therebetween, corresponding subportions of the stored and aligned first and second portions of data are then compared to detect difference therebetween, and upon detecting a difference exceeding a predetermined threshold, the presence of a defect at a particular pixel location on the inspected object is indicated.