1. Field of the Invention
The invention relates to a projection illumination system.
Lithographic methods are conventionally employed for the manufacturing of miniaturized structures and components. Miniaturized components and structures include, for example, integrated circuits, fluid crystal elements, micromechanical components and the like. Hereby, patterns or structures predetermined on a mask (“reticle”) are imaged onto a radiation sensitive substrate, such as, for example, a wafer provided with a radiation sensitive layer (“resist”), by an imaging optics of a projection illumination system. The light required for the imaging is generated by an illumination system of the projection illumination system, which comprises an illumination optics for illuminating the mask.
With the continued trend towards increasing miniaturizing of the components to be manufactured, greater and greater demands are made on the imaging quality of projection illumination systems.
2. Brief Description of Related Art
A projection illumination system is known, for example, from US 2002/0001088 A1, in which particular parameters characterizing the imaging quality can be determined by an interferometric measurement of the imaging optics. An imaging optics is, for example, known from U.S. Pat. No. 5,973,863 which comprises actuators which adjust a position of at least one optical element of the imaging system relative to other elements of the imaging system. Thus it is possible to reduce certain imaging errors of the imaging optics by correspondingly controlling the actuators.
Due to the large number of optical components in a projection illumination system, the imaging quality is determined by a multitude of parameters of the optical components and is also subject to operation related drifts.