Optimization of EUV mask structures for mitigating the forbidden pitch in 5nm node

With the technology node scaling to 5 nm, the forbidden pitch effect caused by destructive interaction between main feature and neighboring feature always leads to poor process window. Due to the small critical dimension (CD) and pitch of these features, forbidden pitches (FPs) become more sensitive in extreme ultraviolet (EUV) lithography. Therefore, controlling of FPs are becoming more and more critical. With the purpose of providing a strategy of mitigating the negative effect of forbidden pitch, an optimization method of the mask structure is developed in this paper. For illustration, three optimal mask structures under quasar illumination conditions are given by the optimized method. The performances of these three structures are demonstrated by the numerical lithography simulator S-litho. The effectiveness and validity of the proposed method are demonstrated from above simulation results. Therefore, the mask structure provided by the optimized method has the potential to be an efficient candidate for mitigating the negative effect of forbidden pitch structure.