Patent ID: 7580113
Filing Date: 2009-08-25
Classification: G03B,G03F

Abstract:
1. A method of reducing a wave front aberration of an optical wave traversing a projection system of a lithographic apparatus constructed and arranged to expose a radiation sensitive layer on a substrate to an image of a pattern, the method comprising: obtaining information on the wave front aberration; calculating an adjustment of an optical element of the projection system for reducing the wave front aberration; and applying the calculated adjustment to the projection system, wherein the calculating includes: obtaining information on a spatial distribution of radiant intensity in a pupil of the projection system as present during the exposure of the radiation sensitive layer, selecting a threshold intensity in a range between maximum intensity of the distribution of intensity and zero, defining areas in the pupil within which a local intensity is higher than the threshold intensity, and limiting the reducing to areas of the wave front corresponding to the areas in the pupil.