| 摘要 |
PURPOSE:To make it possible to execute accurately the decision about the size of a foreign substance by a method wherein the size of a defect is decided on the basis of the number of times of detection of scattered light about the same defect, which can be obtained through overlapped scanning by a light beam. CONSTITUTION:As a laser beam 5 is scanned in such a way as to overlap, the beam 5 is irradiated on the same foreign substance 20 a plurality of times and scattered lights 5a are respectively generated in every irradiation. These scattered lights 5a are detected by a photosensor 9 each time of the generation. If the peak diameter D (half-width) of the laser beam 5 and the pitch P between the scannings are constant, the number of times of irradiation of the laser beam 5 to the foreign substance 20, that is, the number of times of detection of the photosensor 9 maintains a constant correlation between the size of the foreign substance 20 and the number. Accordingly, regardless of the irradiation direction of the laser beam to an actual foreign substance and the position and the material of the photosensor, the decision error about the size of the foreign substance is significantly inhibited. |
