Simulation of Multilayer Defects in Extreme Ultraviolet Masks

We have employed a scalar simulation based on Fresnel formulas to predict approximately how strongly a multilayer defect in a reflective mask affects the aerial image in extreme ultraviolet lithography. This method enables us to obtain the field reflected from a defective mask, using considerably fewer computational resources than those required for a rigorous electromagnetic simulation. This method was applied to two-dimensional masks with multilayer defects modeled by a simple structure in which the coverage profile was identical throughout the layers. For such defects, we confirmed the validity of the scalar simulation by comparing the normalized peak intensity to that obtained from an electromagnetic simulation. The dependence of the printability of a defect on its size and position is also discussed.