| 摘要 |
PURPOSE:To correct detection sensitivity constantly by detecting the change in the detection sensitivity of foreign matter caused by the change in the intensity of laser beam and the up-and-down movement of a mask surface, by providing the reference pattern generating the same optical information as that generated from foreign matter. CONSTITUTION:The laser beam 1a of a laser beam source 1 is deflected to an x-direction by a predetermined angle by a beam deflector 2 and focused to the surface of a mask M as spot beam through an image forming lens 3. The spot beam two-dimensionally scans the surface of the mask M by the beam deflector 2 and a slider 4. Light receiving elements 10, 11, 12 and light condensing lenses 10a, 11a, 12a are arranged and the position of the slider 4 in a y-direction is detected by a length measuring machine. A reference index plate 20 comprising flat glass having the same degree as the mask M is provided to the leading end side of the slider 4. A solid substance having the same size as foreign matter to be detected is adhered as a reference pattern and scattered light same to that from the foreign matter is detected and the correction signal of detection sensitivity is calculated. |
