17 October 2008 Enhanced DCT2-based inverse mask synthesis with initial SRAF insertion
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Abstract
Inverse mask synthesis, or Inverse Lithography Technology, as a next generation resolution enhancement technology, is drawing pretty much attention after years of development. However, the existing optimized mask usually is too complex such that the pattern simplifying procedures have to be applied as a post processing step. But the post processing step may lead to pattern degradation and unwanted side lobe printing. In this paper, we first implement a new inverse mask synthesis system using two dimensional discrete cosine transform(DCT2) of the target mask, where the low frequency components are used in the optimization. As the high frequency components are discarded, the resulted optimal pattern is similar in shape to that of using the level set method in the published papers. Moreover, as inverse mask synthesis is an ill-posed problem, there are some local minimum locations. Previous algorithms usually use the desired pattern as an initial iteration point, in the sense that optimized pattern shall be a perturbation of the desired pattern. A common fact is that initial solution is critical to the optimization procedure and final result. In this paper, we apply an initial SRAF insertion around the main features before starting the existing inverse engine. The SRAF insertion does not need to be as accurate as that in the traditional SRAF+main feature OPC flow. Therefore, it does not add higher time burden on the whole mask synthesis flow. We implement the SRAF insertion based on computed mask electric field distribution. The experimental results show that using the initial fast SRAF insertion, the inverse engine is able to take advantage of a better initial high contrast image distribution, and the optimized pattern can be much simpler while the pattern fidelity is still in good control. We also observe that better optimized patterns can be achieved with fewer iterations.
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Shanhu Shen, Shanhu Shen, Peng Yu, Peng Yu, David Z. Pan, David Z. Pan, } "Enhanced DCT2-based inverse mask synthesis with initial SRAF insertion", Proc. SPIE 7122, Photomask Technology 2008, 712241 (17 October 2008); doi: 10.1117/12.801409; https://doi.org/10.1117/12.801409
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