| 摘要 |
PURPOSE:To accurately monitor by observing a composite image of two observing areas by optical detecting means having observing areas in a positional relation which is parallel to a reference of a wafer holder and is separated by the designing value of the interval of two marks. CONSTITUTION:A light beam (a) from a light source 10 is transmitted by half (b) at a half mirror 8 and reflected by half (c). The transmitted light (b) is fed through a mirror 7 and an enlarging lens system 5 to the observing area 4 of left side of a wafer 2. The light (e) reflected from the area 4 is fed to the observing surface 9 through the opposite route to the incident passage. The reflected light (c) of the mirror 8 is fed through an enlarging lens system 6 to the area 4, and the reflected light (h) is fed to the observing surface 9 through the reverse route. Accordingly, when two marks 3 are disposed at normal position separated by l in parallel with the reference line 1 of the wafer holder, the images of the marks 3 at the right and left entirely coincide on the observing surface 9.
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