| 摘要 |
PURPOSE:To prevent the performance of image formation of a projection lens from being influenced and to send the sufficient quantity of light to a photodetector at the outside by a method wherein optical components such as a small mirror and the like are arranged at the position which is away from the optical center of the projection lens. CONSTITUTION:An image of a slit mark at a reticle 3 is formed on a wafer 7 by the illuminating light 1 for alignment; when the image of the mark illuminates a wafer alignment mark WM, the reflected light or the scattered light is produced. In order to guide, especially, the scattered light to photodetectors installed at the outside, two small mirrors 5a, 5b are arranged on the same plane as a plane ep passing through the optical center 12 of a projection lens 4 and at outside positions (regions at the circumference of the optical center) away from the optical center 12 in such a way that one part of the reflected light and/or the scattered light from the alignment mark WM on the wafer 7 is guided to the photodetectors 6a, 6b, installed at the outside, via condensing lenses 7a, 7b.
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