Patent ID: 6650419
Filing Date: 2003-11-18
Classification: G03F

Abstract:
Interferometric apparatus for measuring changes in altitude between a surface and a datum line, said apparatus comprising:a dimensionally stable metrology frame; at least one photolithographic translation stage for holding a wafer in an exposure position, said photolithographic translation stage being mounted for nominally plane translation with respect to said metrology frame in at least two orthogonal directions while experiencing relatively smaller changes in altitude in a direction nominally normal to said at least two orthogonal directions, said photolithographic translation stage comprising means for defining a datum line in said photolithographic translation stage; elongated reflector means mounted with respect to said metrology frame to provide said surface; and at least one interferometer system mounted at least in part on said photolithographic translation stage for movement therewith, said interferometer system comprising a source, a reference path mounted off said photolithographic translation stage, and a measurement path including a constant deviation prism mounted for movement with said photolithographic translation stage intermediate said source and said elongated reflector means, said source being structured to provide reference and measurement beams for travel, respectively, along said reference and measurement paths to provide a signal containing information that varies in accordance with said changes in altitude between said surface and said datum line as said photolithographic translation stage moves, said elongated constant deviation prism being operative to make said signal insensitive to variations in angular rotation of said photolithographic translation stage at least about one of said two orthogonal directions.