Features in forbidden pitch have limited exposure latitude and depth of focus in lithography exposure. This paper provides an analysis of forbidden pitch in extreme ultraviolet lithography (EUVL) from the perspective of rigorous simulation and source mask optimization (SMO). In the stage of rigorous simulation, S-litho is used to analyze the normalized image log slope (NILS) of test patterns from different critical layer in 5nm node. Then the process windows of these test patterns are simulated and compared by the lithography simulator Proteus WorkBench. From the result analysis, the forbidden pitches of critical layer in 5nm node are summarized. In addition, the strategy of mitigating the negative effect of forbidden pitch is proposed with the help of computational lithography.
Mask defectivity is a critical challenge to the high-volume production of extreme ultraviolet lithography (EUVL). In a similar way to the optical proximity correction (OPC), mask absorber pattern optimization could weaken the impact of defect on lithography. In order to compensate the amplitude and phase impact caused by the defects on the EUV mask blank, an advanced evolution strategy based on genetic algorithm (GA) combining with manufacturing rule check (MRC) is proposed to optimize the mask pattern. The influences of various defects on lithography are firstly summarized from mass simulation results, as well a novel method based on GA is proposed to compensate the negative impact by defects. Finally, the advantages of the proposed method in convergence efficiency and robustness are validated through comparing with differential evolution (DE) and original GA with simulations on contact patterns and logic patterns with the lithography simulator Sentaurus Lithography (Slitho).
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