Pattern inspection apparatus and pattern inspection method inspecting a pattern using an image corrected using offset amount based upon dark noise levels

A pattern inspection apparatus comprising:

• an illumination optical system configured to illuminate an inspection substrate on which a pattern is formed;
• an offset calculation circuit configured to calculate an offset amount based on a difference between a dark noise level Dr1 at an image accumulation time t1 of each of a plurality of photo sensor elements arrayed two-dimensionally and a dark noise level Dr2 in a case that the image accumulation time t1 is switched to an image accumulation time t2 different from the image accumulation time t1;
• a time delay integration (TDI) sensor configured to include the plurality of photo sensor elements, to acquire an image of the inspection substrate by receiving one of a transmitted light and a reflected light from the inspection substrate by the plurality of photo sensor elements, to correct, using the offset amount, a pixel value of optical image data of the acquired image, and to output the optical image data having been corrected;
• and
• a comparison circuit configured to compare an optical image formed by the optical image data output from the TDI sensor with a reference image, wherein
• the offset calculation circuit calculates the offset amount according to an image acquisition timing from the time when the image accumulation time is switched until the dark noise level Dr2 is stabilized, and
• the TDI sensor corrects, for each image acquisition timing, the optical image data by using the offset amount corresponding to the image acquisition timing concerned.