Patent Document ID: 4448532
Application ID: 06249474
Patent Status: 1

Claim One:
1. Optical inspection apparatus for detecting defects in photomasks and the like containing a plurality of supposedly identically configured portions. comprising: first and second detector means disposed in spaced-apart relationship and operative to simultaneously inspect corresponding sub-portions of two of said supposedly identically configured portions and to develop first and second digital signals corresponding to the detected character of each said sub-portion; scanning means for causing relative movement between the photomask and said first and second detector means thereby defining at least one scan line across the photomask being inspected; memory means for storing said first and second digital signals developed as said photomask is scanned; defect detector means for comparing said stored first and second digital signals and for developing defect signals when said stored second signal differs from said stored first signal; first signal processing means including first and second buffer means, said first processing means being operative to generate first and second address data corresponding to said stored first and second signals and to store in said first buffer means those defect signals and address data developed in response to a first scan of said one scan line, and operative to store in said second buffer means those defect signals and address data developed in response to a second scan of said one line; comparator means for comparing the address data of defect signals contained in said first buffer means to the address data of defect signals stored in said second buffer means, and for generating real defect signals when defect signals stored in said first buffer means have a common address which defect signals stored in said second buffer means, and for generating false defect signals each time a defect signal stored in said first buffer means does not have a common address with a defect signal stored in said second buffer means; real defect buffer means for receiving and storing said real defect signals; false defect buffer means for receiving and storing said false defect signals; and utilization means for processing and storing or otherwise utilizing the data stored in said real defect buffer means and said false defect buffer means.