Patent ID: 6674512
Filing Date: 2004-01-06
Classification: G01B,G03F

Abstract:
A method employing an interferometer system to determine the relative position, within a given plane, of a plurality of moveable members, wherein said interferometer system comprises at least one component supporting a plurality of interferometer measurement beams and at least two moveable members, at least one of which is a reference moveable member, the method comprising:directing from each said at least one interferometer component at least two interferometer measurement beams toward said reference moveable member; directing at least two interferometer measurement beams from the at least one interferometer component toward each of said at least two moveable members that are not said reference moveable member; measuring an optical path length change of said at least four interferometer beams as a result of relative movement of said at least one interferometer component and said moveable members; and determining the relative positions of said moveable members based on said measured optical path length changes.