| 摘要 |
Apparatus for detecting the edge of a pattern on an object surface is disclosed. The apparatus includes a light source for emitting a collimated light beam, a condensing optical system for forming an elongated light spot of the collimated light beam on the object surface, an image-forming optical system for forming an image of the elongated light spot by focusing the reflected light from the object surface, a detector for forming an output signal corresponding to the reflected light from the spot image, an image rotator and a driving member. The elongated light spot is formed by means of slit. The direction of the slit is changed by the driving member to change the direction of the elongated light spot on the object surface. The driving member also drives the image rotator so as to keep the direction of the reflected spot image unchanged irrespective of the change of the direction of the slit.
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