Predicting and Correcting for Image Placement Errors during the Fabrication of EUVL Masks

With the stringent requirements on image placement (IP) errors in the sub-65 nm regime, all sources of mask distortion during fabrication and usage must be minimized or corrected. For extreme ultraviolet lithography, the nonflatness of the mask is critical as well, due to the nontelecentric illumination during exposure. This paper outlines a procedure to predict the IP errors induced on the mask during the fabrication processing, e-beam tool chucking, and exposure tool chucking. Finite element (FE) models are used to simulate the out-of-plane and in-plane distortions at each loading step. The FE results are compiled to produce a set of Correction Tables that can be implemented during e-beam writing to compensate for these distortions and significantly increase IP accuracy.