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Effect of central obscuration on image formation in projection lithography

Central obscuration of the pupil is a prominent feature of many high performance reflective designs being considered for sub-200nm lithography. The performance of centrally-obscured designs were investigated using computer simulations of projected image intensity and major features from simulation were experimentally confirmed. The effect of partially-coherent illumination on centrally-obscured systems was studied and an optimized annular illumination system is proposed. 1.