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18 March 2015 Focus shift impacted by mask 3D and comparison between Att. PSM and OMOG
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The impact of mask three dimensions (M3D) effect on lithography processes is getting more pronounced from 32 nm nodes1-2. In this paper, we report four research progresses on the M3Deffect. Firstly, the impacts of M3D effect on the best focus (BF) offset were studied with though pitch as test pattern. The M3D effect has negative impacts on the BF, generating the BF offset pattern by pattern. The BF offset strongly depends on MoSi film thickness (THK). However the impact of MoSi profile, or side wall angle (SWA) could be ignored. Secondly, M3D OPC is needed to mitigate the shift of dose and focus center. Thirdly, as long as enough shade, the thinner MoSi, the less BF shift, as electromagnetic field (EMF) effect makes space behave smaller, which leads to higher contrast but higher mask error enhancement factor(MEEF); So the trade-off between contrast and MEEF is needed. And MoSi THK 43.7 nm in production supposed to be the optimized value from this study. Finally, compared to attenuating phase shifting mask (att.PSM) mask, opaque MoSi on Glass (OMOG) mask is more robust in terms of MEEF, the normalized image logarithmic slope (NILS) etc., not obviously influenced by mask duty ratio.
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Yansong Liu, Xiaojing Su, LiSong Dong, Zhiyang Song, Moran Guo, Yajuan Su, and Yayi Wei "Focus shift impacted by mask 3D and comparison between Att. PSM and OMOG", Proc. SPIE 9426, Optical Microlithography XXVIII, 94261H (18 March 2015);

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