Patent ID: 7436993

Claim:
An apparatus for detecting a defect in a periodic pattern on an object, comprising: an image pickup part for picking up an image of an object; a positional difference acquisition part for acquiring a first positional difference vector between a first image in a first area on an object and a second image in a second area which has the same pattern as that of said first area and acquiring a second positional difference vector between said second image and a third image in a third area which has the same pattern as that of said second area; a differential image generation part for generating a first differential image between said first image and said second image while adjusting a position of said first image relatively to said second image on the basis of said first positional difference vector and generating a second differential image between said second image and said third image while adjusting a position of said second image relatively to said third image on the basis of said second positional difference vector in the same manner as the case of said first positional difference vector; a position adjustment part for adjusting a position of said first differential image relatively to said second differential image on the basis of said first positional difference vector or said second positional difference vector; and a defect detection part for detecting a defect by comparison between said first differential image after position adjustment and said second differential image, wherein said first image, said second image, and said third image are sequentially obtained in said image pickup part, acquiring said third image in said image pickup part and acquiring said first positional difference vector in said positional difference acquisition part are executed in parallel, and acquiring said second positional difference vector in said positional difference acquisition part and generating said first differential image in said differential image generation part are executed in parallel.