13 March 2012 Source-mask optimization incorporating a physical resist model and manufacturability constraints
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Abstract
Lithographic process development at small k1 factors requires source-mask optimization (SMO) for obtaining sufficient process stability. Two prerequisites must be fulfilled to directly employ the SMO solutions for the optimized source and mask layouts: i) the simulation model underlying SMO should accurately predict the printing on wafer, and ii) the mask patterns must be manufacturable. With regard to i), SMO including a properly calibrated physical resist model is assumed to be more predictive across variable source and mask shapes than SMO with a computationally fast but simplifying photoresist treatment. By coupling SMO and rigorous lithography simulations, we effectively incorporate physical resist modelling into SMO. Additionally, concerning ii), we tackle the manufacturability task by incorporating mask rule constraints already during SMO. Optimizing the mask's degrees of freedom in a mask-rule constrained space, we avoid any post-processing of the optimized mask clips and any corresponding degradation of the result quality. The concept of constrained optimization is also extended to placing and optimizing assist features during SMO. We employ virtual assist feature seeds that can only form real assists if mask rules are met. In that way assist features are simultaneously co-optimized together with the main features and the source.We discuss our approach at 2 examples, a line/space array edge and a SRAM cell, and point to reference1 for a rigorous cell optimization for DRAM.
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Thomas Mülders, Thomas Mülders, Vitaliy Domnenko, Vitaliy Domnenko, Bernd Küchler, Bernd Küchler, Hans-Jürgen Stock, Hans-Jürgen Stock, Ulrich Klostermann, Ulrich Klostermann, Peter De Bisschop, Peter De Bisschop, } "Source-mask optimization incorporating a physical resist model and manufacturability constraints", Proc. SPIE 8326, Optical Microlithography XXV, 83260G (13 March 2012); doi: 10.1117/12.914047; https://doi.org/10.1117/12.914047
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