Pattern checking apparatus

Claim 1

A pattern checking apparatus comprising: scanning and imaging means for two-dimensionally scanning a pattern to be checked so as to provide sequential image signals; A/D converter means for converting the image signals sequentially received from said scanning and imaging means into digital image signals; standard data generating means for sequentially generating standard pattern data corresponding to said pattern to be checked; first buffer memory means for temporarily storing the digital image signal received from said A/D converter means; second buffer memory means for temporarily storing the standard pattern data from said standard data generating means; candidate defect detecting means for comparing the digital image signals and the standard pattern data to detect a candidate defect on the basis of detection of anti-coincidence therebetween; a first analyzing memory for storing the digital image signal for a portion of said pattern to be checked inclusive of the candidate defect and signals relating to points around the candidate defect, the entry of the digital image signals into said first analyzing memory being stopped when said candidate defect detecting means detects the candidate defect; a second analyzing memory for storing the standard pattern data for the portion of said pattern to be checked inclusive of the portion corresponding to the candidate defect and signals relating to points therearound; and controlling processor means responsive to detection of the candidate defect by said candidate defect detecting means for reading and comparing the digital image signals stored in said first analyzing memory and the standard pattern data stored in said second analyzing memory to determine the amount of positioning error therebetween when a positioning error exists, for reading at least one of the digital image signals from said first buffer memory means and the standard pattern data from said second buffer memory means while relatively correcting said positioning error, and for entering the relatively corrected digital image signal or standard pattern data into said candidate defect detecting means and said first or second analyzing memory, so that in reading and comparing again the digital image signal stored in said first analyzing memory and the standard pattern data stored in said second analyzing memory, the inclusion of positioning errors as candidate defects is minimized and a candidate defect in a practically allowable error range is removed from the remaining candidate defects, thereby to detect a true defect.