<title>Novel illumination system for EUVL</title>

A concept for a novel arc-field, illumination projection system, particularly for EUVL applications, is presented. This system consists of a light source, a collector, a fly-eye, and a condenser. The fly-eye has two reflectors. One of them is constructed with using arc-shaped, concave mirror elements, the other using many rectangular, concave mirror elements. Both elements are arranged closely side by side. All of the arc-shaped mirrors have a corresponding rectangular mirror on a one-to-one basis. Each rectangular mirror projects its corresponding arc-shaped mirror's images onto an arc projection field on the mask. As a consequence, all of incident rays on fly-eye reflector constructed by arc-shape mirror elements are gathered in the arc projection field. Currently, the main type of illumination system for EUVL is based on so-called 'Koehler-critical illumination,' which is not necessarily proper for a scanner system. Then this system adopts Koehler illumination. It is necessary for scanner illumination systems to have means for minute adjustments of its properties (e.g. irradiance distribution). Such adjustments means are presented.