Reflective alignment position signal producing apparatus

Abstract

A position signal producing apparatus, for an apparatus for project-printing a pattern on a reticle onto a wafer through a project lens system with exposure light, for producing a position signal indicative of the position of the wafer is disclosed, wherein two different frequency components of alignment light whose frequencies are different from that of the exposure light are interfered with each other at a position alignment blank to form interference fringes having a given pitch. The interference fringes are projected onto a diffraction grating through an achromatizing optical system and the project lens system. Diffracted light returning from the diffraction grating is received by a photodetector which provides a light beat signal. A position deviation signal obtained by phase comparison of the light beat signal provides position alignment by controlling relative positions between the position alignment blank and the diffraction grating. Two light beams of the two different frequency components split by a polarized beam splitter are equalized in image converting condition, or image aspect, by a mirror, so that an accurate mixing of the two frequency components of light beams is performed at the position alignment blank.