Rigorous simulation of mask corner effects in extreme ultraviolet lithography

Abstract

A windowing and multilayer acceleration methodology for rigorous electromagnetic analysis of extreme ultraviolet masks in three dimension is introduced and used to explore strong feature asymmetries associated with off-axis illumination. Specifically synthesizing large features from smaller simulation domains and replacement of the multilayer substrate by upward radiating equivalent sources are used and allow mask corner effects to be analyzed in 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. With 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 effect is associated with diffraction of the upward reflected light and its propagation in the presence of the side wall of the mask edge profile.