Patent ID: 7990520

Claim:
An illumination system, comprising: an illumination optics designed so that, during use, the illumination optics can guide light from a radiation source to an object field in an object plane; an illumination-angle sensor element designed so that, during use, the illumination-angle sensor can determine an actual illumination-angle distribution of a projection exposure apparatus in a field plane of the illumination optics; an illumination-angle evaluation device comprising a signal connection to the illumination-angle sensor element, the illumination-angle evaluation device being designed so that, during use, a nominal illumination-angle distribution is stored via the illumination-angle evaluation device; an illumination-angle control device comprising a signal connection to the illumination-angle evaluation device, the illumination-angle control device being designed so that, during use, the illumination-angle control device generates an illumination-angle control signal depending on a difference between the actual illumination-angle distribution and the nominal illumination-angle distribution; and at least one movable illumination-angle diaphragm device comprising a signal connection to the illumination-angle control device, the at least one movable illumination-angle diaphragm device being configured so that, during use, the at least one illumination-angle diaphragm device can move at least one illumination-angle diaphragm body to achieve an adjustable, partial attenuation of the light in an area of a pupil plane of the illumination optics, wherein: the illumination system is an EUV microlithography illumination system; and the illumination-angle sensor element is configured so that, during use of the illumination system to illuminate the object field, the illumination-angle sensor monitors the actual illumination-angle distribution of the light.