Mitigation of extreme ultraviolet mask defects by pattern shifting: Method and statistics

Currently the mask blanks used in extreme ultraviolet lithography cannot be fabricated free of defects. A rapid method of determining the optimum placement of mask patterns on the blank to avoid these defects is described. Using this method, the probability of fabricating defect-free masks, when the pattern is (1) randomly placed on the mask blank or (2) positioned optimally to avoid defects, is determined for a variety of integrated circuit designs, defect densities, and defect sizes. In addition to circular defects, oval and clusters of defects are also considered. Finally, simple analytical expressions for the probability of obtaining a defect-free mask in the case of random placement of the mask pattern is presented and compared to Monte Carlo simulations. © 2012 American Vacuum Society.