Patent ID: 6885450

Claim:
An optical positional deviation detecting apparatus for optically detecting a positional deviation in alignment between a first mark and a second mark of a measurement mark configured by forming the second mark on the first mark, comprising: an irradiation optical system for irradiating the measurement mark with a beam of irradiation; an image forming optical system for forming an image of the measurement mark by converging reflected beam from the measurement mark; an imaging device for photographing the image of the measurement mark, which has been formed by said image forming optical system; an image processing device for measuring the positional deviation in alignment between the first mark and the second mark by processing an image signal obtained by said imaging device; and a field stop provided on said irradiation optical system; and a field stop position adjustment mechanism for adjusting a position of said field stop, in a plane perpendicular to the optical axis, while maintaining a size of the image field fixed; wherein said field stop position adjustment mechanism adjusts the field stop position on the basis of an asymmetric focus characteristic of a line and space mark pattern image obtained when forming the image of a line and space mark pattern within an image field area of said imaging device.