| 摘要 |
PURPOSE:To detect the position of focussing excellently, and to improve reproducibility by removing a resist layer on a mark section on a wafer while lighting marks on both a reticle and the wafer and variously changing the imaging optical path length of detected beams when detected beams from each mark are to be detected and the images of the mark on the reticle and the mark on the wafer are observed. CONSTITUTION:A plurality of glass plates 50A or 50E, thickness TA or TG of which each differ, are mounted respectively to a transparent rotating plate 50, and the glass plate 50A or 50E are inserted into an optical path and optical path length is changed gradually when the transparent rotating plate 50 is turned. The position of focussing is altered centering around the position of an image sensing surface in a TV camera 56. When a reticle R and a wafer W are not positioned at the positions of focussing to a projection lens 18, thc peak points of graphs GA, GB are displaced in response to the quantity of out of focussing. The quantity of displacement Z corresponding to the quantity of out of focussing Z of the reticle R and the wafer W is input to a main control system 60 as a TTL focussing-displacement signal TFS from a focussing detector 58, and required offset is applied to the detecting focussing position of an AF light reception system 34, thus compensating the quantity of the displacement.
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