Patent ID: 7443485
Filing Date: 2008-10-28
Classification: G03F

Abstract:
1. A method of measuring apodization of projection optics for use in a lithographic apparatus, the projection optics having an object plane where, in use, a patterning device is located, a pupil plane, and an image plane where, in use, a substrate is located, the method comprising: placing an aperture in said object plane to create a substantially uniform radiation distribution; illuminating the aperture in said object plane; measuring an intensity distribution at a plane which is conjugate to the pupil plane in order to calculate the apodization of the projection optics; placing an aperture at the image plane of said projection optics to create a substantially uniform radiation distribution; placing a sensor behind said aperture at the image plane seen from the projection optics in a plane out of focus with respect to the image plane of said projection optics; and calibrating the angular sensitivity of said sensor.