Projection optical device

Abstract

Abstract PURPOSE:To detect accurately the focusing of a projection mask pattern image on a projected body such as a wafer by detecting the focusing on the projected body on the basis of an image signal corresponding to the image formation state of an overlap image between a light image of a mask pattern and a reflected light image projected reversely from the projected body. CONSTITUTION:The mask R with a light-absorbent and light-shielding mark M is lighted up and the reflected light image of the mark M projected reversely from a wafer W and the light image of the mark M formed by illumination light form an overlap image on the photodetection surface of a TV camera 12. In this case, calibration is so performed that the output of a projector 13 and a photodetector 4 which detect in-focus image formation corresponding to the image signal from a camera 12, etc., is 0; when the mask pattern projection image on the wafer is in focus, that is detected accurately with the output of the photodetector 14 which varies according to the upward/downward movement of a stage 11.

Inventors

• 👤 Kyoichi Suwa
• 👤 恭一 諏訪

Bibliographic Details