Design of a high-numerical-aperture extreme ultraviolet lithography illumination system

High-numerical-aperture (NA) anamorphic imaging projection objectives are the industrial choice for extreme ultraviolet lithography under the advanced technology node. The illumination system has to match the elliptical entrance pupil of the high-NA projector. In this paper, an illumination system suitable for a high-NA anamorphic projection objective is designed. The two-mirror relay system of the illumination system is designed by a two-stage process. The first-order initial configuration with spherical surfaces is calculated by a method based on matrix optics. Then after tilting and decentering the two spherical surfaces to eliminate obscuration, the two mirror surfaces are fitted into conic surfaces. To realize many different illumination modes, a facet mirror matching method based on combinatorial optimization is proposed to allocate the mapping relationship between the field and pupil facets under different illumination modes. Simulation results of the system illumination uniformity show the system can achieve high uniformity on the reticle under different illumination modes.