Patent ID: 6958806

Claim:
A lithographic apparatus comprising: a radiation system to provide a projection beam of radiation, the radiation system comprising an illumination system for defining a position dependent intensity distribution of the beam in a pupil plane; a support structure for supporting a patterning structure, the illumination system defining an angle dependent intensity distribution of the beam at the patterning structure dependent on the position dependent intensity distribution in the pupil plane; a substrate table for holding a substrate; a projection system for projecting the patterned beam onto a target portion of the substrate; a beam splitter positioned in a path of the projection beam during operation of the lithographic apparatus, the beam splitter splitting off an auxiliary beam; a detector with a detection element disposed in a path of the auxiliary beam so as to detect information about a position dependent intensity distribution corresponding to the pupil plane; and a controller having an input coupled to said detector and an output coupled to said illumination system, wherein the controller is configured to receive detected information from said detector and to provide a feedback to said illumination system to control a parameter of the illumination system.