Method of determining at least one parameter that is characteristic of the angular distribution of light illuminating an object in a projection exposure apparatus

摘要

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 is described. This parameter may be, for example, a pupil asymmetry. The method comprises the step of inserting a filter element in or in close proximity of a pupil plane of an illumination system that is arranged between a light source and the object. The filter element has a filter function that varies in an azimuthal direction with respect to the optical axis of the illumination system. Then the intensity of the light in a plane downstream of the pupil plane is measured. After rotating the filter element around the optical axis by an angle &PHgr;, the measurement of the intensity is repeated. From the filter function, the angle &PHgr; and the measured intensities the parameter is measured.