Analysis of modes in periodic EUV mask structures using a Bloch–Floquet-based analytical modal approach

Accurate modeling of EUV mask structures is essential for predicting imaging performance in next-generation lithography. This work presents a model with an analytical modal framework based on Bloch–Floquet theory to describe periodic EUV mask absorbers as coupled waveguide arrays. The approach captures lateral mode coupling and periodic boundary conditions while maintaining high computational efficiency and physical interpretability. Mode excitation coefficients and diffraction efficiencies are obtained analytically through overlap integrals and modal projections. The model investigates how absorber refractive index, geometry, and thickness influence mode behavior and diffraction characteristics. Comparison with RCWA highlights the model’s accuracy and helps identify its possible limitations.