Fast rigorous model for mask spectrum simulation and analysis of mask shadowing effects in EUV lithography

A fast rigorous model is developed for the simulation of mask diffraction spectrum in EUV lithography. It combines a modified thin mask model and an equivalent layer method and provides an analytical expression of the diffraction spectrum of mask. Based on this model, we propose a theoretical analysis of the mask shadowing effect. Mathematical expressions for the best mask (object space) focus position and for the required correction of mask pattern size are derived. When the mask focus is positioned in the equivalent plane of the multilayer, the amount of pattern shift is reduced. When the mask pattern size is corrected using the derived formula, taking a space pattern with the target CD of 22 nm as an example, the imaging CD bias between different oriented features is below 0.3 nm.