Mask diffraction analysis and optimization for extreme ultraviolet masks

We employ a direct analysis of the intensity and the phase of the diffracted light by rigorous electromagnetic field (EMF) simulations to investigate mask-induced imaging artifacts in EUV lithography. Analysis of the diffraction efficiencies and phase differences between the diffraction orders versus mask and illumination parameters is used to explore EUV-specific imaging artifacts such as feature-orientation-dependent placement errors and feature sizes, shifts of the best focus position, process window asymmetries, and other aberration-like phenomena. The results of these simulations aim to understand the reason for these EUV-specific imaging artifacts and to devise strategies for their compensation. Finally, rigorous EMF models of light scattering from EUV masks are applied to identify ideal mask absorber stacks using global optimization techniques.