Patent ID: 7379190

Claim:
A lithography system, comprising: a stage for supporting a wafer; an illumination system including a radiation source and a lens assembly, wherein the illumination system is configured to direct radiation through a mask to produce spatially patterned radiation, and the lens assembly is configured to image the spatially patterned radiation onto the wafer; a first interferometry system configured to monitor a location of the stage within the lithography system as the stage moves relative to the illumination system; a second interferometry system comprising an interferometer configured to direct two beams from a common light source along different paths to a surface associated with the stage, the second interferometry systems being configured to identify an alignment feature on the surface associated with the stage based on an output beam formed from light from the two beams specularly reflected from the alignment feature; and an electronic controller coupled to the interferometry systems, wherein the electronic controller is configured to determine information about a location of the stage when the alignment feature is identified.