Reticle inspection system

Abstract

An automatic inspection system including an illuminator for illuminating a reticle or photomask to be inspected, while optically projecting a magnified image of the reticle or photomask onto a plurality of detector elements. A carriage assembly moves the object at a constant velocity to allow the detector elements to sequentially view the entire surface to be inspected. The detector elements are responsive to the intensity of light incident thereupon and are periodically scanned to obtain a two-dimensional measured representation of the object. A database adaptor formulates a two-dimensional representation from the design database description corresponding to the scanned object simultaneously and in synchronism with the scanning of the photomask or reticle. The measured and database adapted representation of the scanned object are input to a signal processor for alignment and defect detection. While the representations are shifted through a memory, an alignment circuit dynamically measures and corrects for misalignment between the representations, so that a defect detector can effectively compare the representations for defects. Additional correction of misalignment between the representations is obtained by modulating the size of the measured representation as detected by the detector elements. At the operator's option, a second measured image of a multi-cell reticle or photomask may be used for comparison as a substitute for the database representation.