Patent ID: 6985218
Filing Date: 2006-01-10
Classification: G03F

Abstract:
1. A method of determining at least one parameter that is characteristic of the angular distribution of light illuminating an object in a projection exposure apparatus, said method comprising the following steps: a) insertion of a filter element in or in close proximity of a pupil plane of an illumination system arranged between a light source and the object, said filter element having a filter function that varies in an azimuthal direction with respect to the optical axis of the illumination system; b) measurement of the intensity of the light in a plane downstream of the pupil plane; c) rotation of the filter element around the optical axis by an angle Φ; d) re-measurement of the intensity of the light in a plane downstream of the pupil plane, e) calculation of the at least one parameter from the filter function, the angle Φ and the intensities measured in steps b) and d).