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Computation of reflected images from extreme ultraviolet masks

With EUV lithography emerging as a promising technology for semiconductor device fabrication with critical dimensions <EQ 100 nm, it is of importance to understand the image formation process in detail. The proposed setup includes a reflective mask consisting of an absorbing material over- coated on a stack of multilayers and 4X de-magnifying optics. In this paper we consider the reflective mask alone i.e. excluding the condenser system and the optics and characterize the reflective properties of the extreme ultra violet mask. In particular, we show the effects caused due to diffraction, non-uniformities in the multilayer stack due to substrate defects, and partial spatial coherence. Several simulation examples are presented.