Design of an illumination system for high numerical aperture anamorphic extreme ultraviolet projection lithography.

The illumination system design for high numerical aperture (NA) anamorphic objectives is a key challenge for extreme ultraviolet lithography. In this paper, a reverse design method of the off-axis mixed-conic-surface-type relay system and an automatic arrangement method of field facets are proposed to design a high NA anamorphic illumination system. The two off-axis relay mirrors are fitted into different conic surfaces based on the conjugation of the mask plane and field facet and that of the illumination exit pupil and pupil facet. To eliminate ray obscuration between neighboring field facets, the field facets are automatically arranged according to the distances that are determined by the relative tilt angles of neighboring field facets under the current illumination mode. The proposed methods are applied in the design of an illumination system matching the NA0.60 anamorphic objective. Simulation results show that the uniformity of the scanning energy distribution can reach 99% on the mask plane under different illumination modes.