Imaging impact of multilayer tuning in EUV masks, experimental validation

Abstract

This paper reports on the experimental validation of adapting the multilayer periodicity of an EUV mask to mitigate pattern shifts at wafer level. This EUV specific pattern shift will eventually contribute to overlay budgets which continue to tighten with decreasing technology node. A good understanding of its manipulators, i.e., mask 3D effects, is paramount. By means of mask diffractometry and scanner exposures at numerical aperture of 0.33 the mask-induced pattern shift at wafer level is verified. These measurements are then correlated to rigorous simulations using a calibrated EUV mask stack model to accurately predict the imaging impact of multilayer tuning in EUV masks. A comprehensive interpretation of the mask 3D impact on pattern shift at wafer level will be presented based on simulated diffraction pupils supported by experimental verification at both mask and wafer level.