Patent ID: 7032208

Claim:
A defect inspection apparatus comprising: a stage on which a plate to be inspected having a circuit pattern is mounted and which is movable in an X direction and in a Y direction perpendicular to the X direction; a sensor which optically scans the circuit pattern to obtain scanned image data; a scanned image data memory which stores the scanned image data in digital form; a normal image data generator which generates normal image data expressed by use of multiple values based on computer-aided design data relating to the circuit pattern; a reference data generator which corrects the normal image data to generate reference data, the reference data generator including a positional corrector which corrects a position data of the normal image data, a filtering part which subjects the normal image data to a filtering process, and a filter coefficient selector which has a plurality of sets of filter coefficients, selects one of the sets of filter coefficients and extracts a desired filter coefficient data used in the filtering part from the one selected from the plurality of filter coefficient sets; and a comparator which compares the reference data with the scanned image data, wherein the filtering part comprises a first finite response filter having substantially symmetrical coefficients and a second finite response filter having a first-order lag function, the first and second finite response filters having respective transfer functions which are subjected to convolution.