| 摘要 |
PURPOSE:To control a gap easily with high accuracy by mounting a diffraction grating to a first body, the gap thereof must be controlled, and a reflective surface to a second body and detecting the gap between both bodies from the intensity of diffracted beams diffracted and reflected by these diffraction grating and reflective surface. CONSTITUTION:Beams projected onto a diffraction grating mark 11 prepared on a mask 10 are reflected by a reflecting makr 14 prepared on a wafer 13 held on a wafer stage 12, and pass through the diffraction grating mark 11 again. Beams diffracted and reflected by both these marks are changed into a large number of plus and minus diffracaed beams diffracted in the direction symmetrical to incident beams. Plus and minus primary diffracted beams in a large number of diffracted beams are reflected by a half mirror 15, and each introduced to photodetectors 17, 18 by condenser lenses 16. Plus and minus primary diffracted beams are converted into diffracted-besm intensity I+1 and I-1 in a photoelectric manner by the photodetectors 17, 18, and signal-processed by a signal processing control section 19 and turned into driving signals for a mask stage 9 and the wafer stage 12, thus controlling a gap between the mask and the wafer. |
