Kla Instruments Corporation

Peter G Eldredge

Mark Joseph Wihl

David A Joseph

William H Broadbent, Jr

Steve Buchholz

An automatic inspection system for inspecting holes in a mask including carriage means 30, illumination means 44, optical means 48, photosensitive detector means 46, and signal processing means 56. The mask 34 to be inspected is positioned by the carriage means in a horizontal plane. The optical means projects a focused image of a portion of the mask onto the photosensitive detector means. Photodiodes in the detector means are responsive to light from the illumination means that is transmitted through the holes in the mask. The signal processing means scans the outputs of the photodiodes and stores in memory a digital representation of the mask. The signal processing means performs inspection measurements and comparison tests. A smoothness checker circuit 240 measures the local radius of curvature of each hole at several places and compares the measurements to predetermined curvature limits to detect nicks and sharp protrusion defects. An area check circuit 246 measures the area of the hole and compares it to predetermined area limits. A diameter check circuit 244 measures the diameter of the hole in two dimensions and compares it to predetermined diameter limits. If either the hole area or the hole diameter is outside their respective limits, a hole size defect is indicated. Means are also provided for locating completely blocked, mispositioned or unintended holes by comparing detected information to a data base.

Automatic system and method for inspecting hole quality

A method and apparatus for receiving two sets of digitized scan data from two optical detectors which simultaneously scan two supposedly identical portions of a photomask for comparing the two sets of scan data to detect defects, and for evaluating the defect data to determine whether or not it represents real defect information or false defect information. Scan lines containing defect data are scanned twice to produce two sets of defect data and the two sets are then compared to produce a real defect data set including only defects detected in both scans. False defects are thus eliminated from the final data set.

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Santa Clara, CA, United States of America

Peter G Eldredge