Rigorous simulation of mask corner effects in extreme ultraviolet lithography

A windowing and multilayer acceleration methodology for rigorous electromag netic analysis of extreme ultraviolet masks in three dimension is introduce d and used to explore strong feature asymmetries associated with off-axis i llumination. Specifically synthesizing large features from. smaller simulat ion domains and replacement of the multilayer substrate by upward radiating equivalent sources are used and allow mask corner effects to be analyzed i n about 10 h on a 200 MHz workstation. Windowing synthesizes the fields for a large mask feature from simulation of smaller domains such as corners. W ith off-axis illumination at angles of even a few degrees, hot spots in the near field occur at edges of the mask which face the illumination. This ef fect is associated with diffraction of the upward reflected light and its p ropagation in the presence of the side wall of the mask edge profile. (C) 1 998 American Vacuum Society.