Patent US 5,840,595

A method of calibrating a pattern inspection device including the steps of determining a first position of a pattern formed on a substrate by holding the substrate on a stage with a first orientation and by illuminating the substrate by means of an optical system of the inspection device, determining a second position by holding the substrate on the stage with a second, different orientation and by illuminating the substrate by the foregoing optical system, and by comparing the first and second positions thus obtained. In each of the foregoing steps for detecting the first and second positions, two opposing edges of the pattern are detected from an image acquired from the substrate, wherein the first and second positions are determined as a midpoint of the two opposing edges.