| 摘要 |
PURPOSE:To inspect the adhering condition of a foreign substance quickly by a method wherein a light beam is applied to a light-permeable plate-shape object and the intensity of the diffractive light produced on one surface and the intensity of the diffractive light produced on another surface are compared and processed. CONSTITUTION:A photomask 5 is placed on a placing table 9, supported only at the circumference, as a tested object. A beam 1 from a laser source 8 is applied to the upper surface of the mask 5. Photodetecting elements 11, 13 which detect a diffractive light produced by a foreign substance on the mask 5. The photodetecting element 11 detects the diffractive light produced on the front surface of the mask 5 and the photodetecting element 13 detects the diffractive light produced on the back surface of the mask 5. The outputs of the two photodetecting elements 11, 13 are compared and the adhering condition of the foreign substance such as the surface on which the foreign substance is adhered or the shape of the foreign substance is judged according to the amplitude of the difference between those outputs. With this constitution, the adhering condition of the foreign substance on the tested object can be inspected quickly.
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