Smoothing based fast model for images of isolated buried EUV multilayer defects

A new fast-CAD imaging model for buried extreme ultra violet (EUV) mask defects is presented that exploits the smoothing process used to mitigate buried EUV multilayer defects. Since the characteristics of the smoothing process dictate nearly identical surface shapes for all defects a single parameter, the peak height of the final profile, is sufficient to predict the projection printed image for an arbitrary buried defect. Data is presented on the effect of smoothing on the reflected field and final wafer image. The degree of similarity among defects with different initial heights, widths and shapes is explored. A compact algebraic model to predict the aerial image dip strength is developed that depends only on the surface height of the EUV mask blank. This model is then integrated into a standard perturbation model for defect feature interaction, and the importance of accounting for absorber features shadowing of buried defects is demonstrated.