Position signal producing apparatus.

摘要

A position signal producing apparatus, for an apparatus for project-printing a pattern on a reticle (1) onto a wafer 82) through a project lens system (4) with exposure light (8), for producing a position signal indicative of the position of the wafer is disclosed, wherein two different frequency components (f1, f2) of alignment light (10) whose frequencies are different from that of the exposure light are interfered with each other at a position alignment blank (5) to form interference fringes (19) having a given pitch. The interference fringes are projected onto a diffraction grating (6) through an achromatizing optical system (18) and the project lens system. Diffracted light returning from the diffraction grating (6) is received by a photodetector (24) which produces 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 (5) and the diffraction grating (6). Two light beams of the two different frequency components split by a polarized beam splitter (12) are equalized in image converting condition, or image aspect, by a mirror (60), so that an accurate mixing of the two frequency components of light beams is performed at the position alignment blank. <IMAGE>