Patent ID: 6819400
Filing Date: 2004-11-16
Classification: G01D,G03F

Abstract:
A lithographic projection apparatus, comprising:a radiation system constructed and arranged to provide a beam of radiation; a support structure constructed and arranged to support a patterning device, the patterning device constructed and arranged to pattern the beam according to a desired pattern; a substrate table constructed and arranged to hold a substrate; a projection system, comprising at least one optical element, constructed and arranged to project the patterned beam onto a target portion of the substrate; and a displacement measuring system constructed and arranged to measure the position of the at least one optical element, wherein the displacement measurement system comprises a first diffraction grating mounted on the at least one optical element and an associated second diffraction grating mounted on a reference frame, and one of the first and second diffraction gratings is arranged to receive diffracted light from the other diffraction grating.