PURPOSE: To stably detect a minor defect by detecting an ideal difference picture optically synthesized from pictures taken by changing interference signals and interference conditions generated when the optical images of patterns are synthesized as signals by means of a photoelectric conversion means.
CONSTITUTION: After moving an X-Y stage 20 to a no-pattern part of a wafer, a picture calculating section performs initial operation of calculating the coherency distribution in the visual field from the interfered picture of the no-pattern section and three signals on the two split optical paths of an interference optical system while the adjustment interference optical system is left fixed. Then, by setting the stage 20 to an inspecting position, the interfered picture is detected from a sensor 4 and bright visual pictures before interference are detected from sensors 4a and 4b and the picture calculating section synthesizes an ideal difference picture by calculation from the detected pictures and coherency distribution. A defect discriminating section detects a defect by using the ideal difference picture.
HIROI TAKASHI
MAEDA SHUNJI
MAKIHIRA HIROSHI
KUBOTA HITOSHI
