Patent ID: 8334983

Claim:
A lithographic apparatus comprising: a support constructed to support a patterning device, the patterning device being capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and, an optical encoder measurement system including an irradiation system configured to direct an irradiation beam to a first scale; optics configured to direct a primary diffracted beam diffracted from the first scale upon irradiation by the irradiation beam to a second scale; and, a detector configured to detect a secondary diffracted beam resulting from a second diffraction of the primary diffracted irradiation beam on the second scale to measure the position of the first scale with respect to the second scale, wherein the optics are mounted on a mover that is movable relative to the irradiation system, or the detector or both the irradiation system and the detector.