Patent ID: 7436502

Claim:
A method of measuring angular intensity distribution of an illumination beam produced by an illumination system of a lithographic apparatus having an illumination system which is configured to condition a radiation beam and to focus the radiation beam in an object plane, a support constructed to support a patterning device for imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam, a substrate table constructed to hold a substrate and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, comprising: placing a detector downstream of said projection system, and measuring an intensity distribution of radiation from said illumination system at said detector to produce a first measurement; placing a first optical element above said object plane which causes radiation from said illumination system to be deflected in a first direction, and measuring an intensity distribution of said radiation deflected by the first optical element at said detector to produce a second measurement; placing a second optical element above said object plane which causes radiation from said illumination system to be deflected in a second direction, and measuring an intensity distribution of said radiation deflected by the second optical element at said detector to produce a third measurement; and using said first, second and third measurements to determine the change in intensity in said first and second directions, and the angular intensity distribution of said illumination beam.