| 摘要 |
PURPOSE:To prevent the degradation in S/N by scattered light and unnecessary diffracted light by forming the outer peripheral edge part of a mark to a curved shape so as to disperse the regular reflected and scattered light from the outer peripheral edge part. CONSTITUTION:The luminous flux emitted from a light source 17 is reflected by a reflecting mirror 18 via a projecting lens system 6 and is projected to a grating lens 15 whose peripheral shape is arc-shaped from the diagonal direc tion, provided on an object 2. This lens 15 has a condensing effect and the exit light is condensed to the point of a prescribed distance from the lens 15. The luminous flux diverged from this point is made incident to a grating lens 16 provided on the object 3 disposed at a prescribed distance. This lens 16 has the condensing effect similar to the lens 15 and the exit light from the lens 16 is passed through the lens 15 and is then condensed to a detecting sur face 14 by a condenser lens 7. The S/N by the scattered light and the unneces sary diffracted light is improved in this way. |
