Patent ID: 7352473

Claim:
A lithographic projection apparatus, comprising: a radiation system configured to provide a beam of radiation; a support configured to support a patterning device, the patterning device configured to pattern the beam of radiation according to a desired pattern; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate; and an interferometric displacement measuring system configured to measure displacements of a moveable component of the apparatus and comprising a model, the model relating sensor measurements to displacements of the moveable component, wherein the model incorporates at least one correction term that is a function of a variable representing beamshear of a measurement beam of the interferometric displacement measuring system, and the interferometric displacement measuring system is configured to determine displacements as a function of moveable component rotation and moveable component position, and to determine interferometer model parameters, including coefficients for terms dependent on a variable representing beamshear of a measurement beam, using a least square fit.