Abstract: An apparatus and method for measuring displacement includes a light beam directed to an interferometer core that splits the light beam into first and second component beams. The first component beam is directed to a diffraction grating at approximately a Littrow angle. A diffraction is received by the interferometer core and is combined with the second component beam. The combination of the first and second component beams is measured to determine displacement of the diffraction grating.

Abstract: An interferometer and corresponding system are provided having several aspects. In a first aspect, there is provided an interferometer adapted to receive separate first and second beams f1 and f2 therein, the interferometer comprising substantially equivalent and separate first and second optical pathways for the first and second beams f1 and f2. In a second aspect, there is provided an interferometer adapted to receive as separate inputs therein first and second beams f1 and f2, where such beams are not mixed or combined until just prior to being output by the interferometer. In a third aspect, an interferometer is provided having one or more beam blockers for intercepting extraneous or undesired light, and keeping such light from contaminating or interfering with separate beams f1 and f2.

Abstract: A system and method for acquiring position information of a movable apparatus relevant to a specific axis is disclosed. In one embodiment, an interferometer generates first and second beams and various beam-steering members are located to define beam path segments for the two beams, but no beam path segment varies in length in unity with displacements of the movable apparatus along the specific axis. In another or the same embodiment, each beam path segment in which the first beam either impinges or has been reflected from the movable apparatus is symmetrical to a corresponding beam path segment of the second beam. The movable apparatus may be a wafer stage in which the “specific axis” is the exposure axis of a projection lens, but with all optical members which cooperate with the stage being located beyond the ranges of the wafer stage in directions perpendicular to the lithographic exposure axis.

Abstract: The position of a stage is determined. Images of a plurality of targets located on the stage are captured. The captured images of the plurality of targets are compared with stored images to determine displacement coordinates for each target. The displacement coordinates for the targets are translated into position coordinates for the stage.