Patent ID: 8937707
Filing Date: 2015-01-20
Classification: G03F

Abstract:
1. A lithographic apparatus, comprising: a movable object, the movable object configured to move in at least first and second directions, the first and second directions being mutually orthogonal and rotatable about an axis perpendicular to the first and second directions; a positioning system operable to move the movable object in at least the first and second directions; an interferometric displacement measuring system operable to measure displacements of the movable object in the first direction and angular position of the movable object about the axis using a measurement beam of radiation, the interferometric displacement measuring system including a reflector, the reflector being substantially planar and substantially perpendicular to the first direction; a control system operable to control the positioning system and the interferometric displacement measuring system to obtain a first set of measurements of the angular position of the movable object, effect a phase offset in the measurement beam and obtain a second set of measurements of the angular position of the movable object; and a calibration system operable to calibrate the interferometric displacement measuring system on the basis of the first and second sets of measurements.