LITHOGRAPHIC APPARATUS, DEVICE MANUFACTURING METHOD, AND METHOD OF CALIBRATING A DISPLACEMENT MEASURING SYSTEM

摘要

An interferometric displacement measuring system operable to measure displacements of a movable object of the lithographic apparatus in a first direction using a measurement beam of radiation and a reflector. The reflector being substantially planar and substantially perpendicular to the first direction. Calibration is obtained using a first set of measurements of the angular position movable object. A phase offset in the measurement beam is affected. A second set of measurements of the angular position of the movable object is obtained. The interferometric displacement measuring system is calibrated based on the first and second sets of measurements.