Simulation of multilayer defects in EUV masks

An extreme ultraviolet (EUV) mask consists of a substrate coated with a reflective multilayer and a patterned absorber layer on top. Particles and bumps on the substrate can cause structural disorder in the multilayer, resulting in multilayer defects. Particles generated during deposition are another possible a source of such defects. Since these defects are virtually impossible to repair, they are the most serious problem in EUV mask fabrication. To determine whether or not a defect is printable, the reflected field in the plane of the mask must be known. This can be calculated rigorously by means of electromagnetic simulation, but the massive computing power required makes this method impractical for 3-dimensional analysis. In this study, we devised a simple simulation method based on Fresnel formulas to calculate the amplitude and phase shift for multilayer defects.