| 摘要 |
PURPOSE:To detect the reflection data on projected image with high precision by a method wherein, within the title focussing position detector, the reflected light on a pattern plate is prevented from entering into a detection optical system so as to reduce the background to the detection signal of any detected light. CONSTITUTION:A mask 3 is opposed to an XY stage 7 for mounting an exposed body through the intermediary of a projection optical system 2. A fiber cable 4 leading illuminating light emitted from a light source 5 to a pattern plate 1 is specified to be a transmitted and detected light separation type so that the reflected light on the end of the cable 4 may not advance toward a detector 6 side. Besides, the differential phase of positive reflected light in transmission part 1a and flare stop part 1b on the pattern plate 1 is set up to be 180 deg.. In such a constitution, the positive reflected light of the illuminating light emitted from the light source 5 and projected from the fiber cable 4 interfere with each other to offset the amplitude up to the level of differential strength between them thereby enabling the background at the photoelectric output from the detector 6 to be reduced by the offset amplitude. |
