JP2830430B

PURPOSE:To remove the stray light generated by the transmitted light of a pellicle and to allow the detection only by the scattered light from foreign matter by selecting one wavelength from plural light beams varying in wavelength. CONSTITUTION:The light beams from light sources 14, 15 are made incident nearly parallel on the pellicle 1 and form band-shaped irradiated parts 5 to 7 in the X direction of the pellicle surface. The incident angle of both the light beams, i.e., the angle formed with the pellicle plane, is set nearly zero. The scattered light 4 is generated and is condensed by an imaging lens 8 when the foreign matter 3 exists on these light beams 5, 6, 7. Since this light is imaged on the photodetecting surface of a photoelectric detector 18, the foreign matter 3 is detected in this way. The light scattered from only the foreign matter is detected by the photoelectric detector 18 without receiving the influence of the frame scattered light by the beam transmitted through the pellicle if the wavelength at which the light beams are mostly reflected on the pellicle surface according to the spectral characteristics of the pellicle is selected by moving the shutter 13.