| 摘要 |
PURPOSE:To enable to eliminate the influence by the back surface of a substrate or a pellicle film, etc. on the detection of obstacles by setting up a slit which shields a scattered light, placing the slit in inclination against the optical axis of a condenser lens, and thus shielding the light in the state of image formation. CONSTITUTION:The slit 13 is set up between the condenser lens 12 and a light receiving element 14, and the scattered light obtained from the part other than above the substrate is shielded, thus enabling to detect only the foreign matter existent on the substrate. The ratio of discrimination is secured by inclining the slit so as to lay along an image formation surface 18, and it is enough to deform the shape of the slit in order to increase the allowable value for the staggering of spots in the direction of X. The slit is provided between the condenser lens 12 and the light receiving element 14, but, actually it is better to further provide a condensing field lens 25 between the slit 23 and the light receiving element 14. |
