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22 March 2012 Quantification of shot noise contributions to contact hole local CD nonuniformity
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As feature sizes continue to shrink, the discrete nature of light and matter is becoming a significant contributor for the variations observed in lithography in general and for EUVL in particular. Owing to the 15x higher energy of EUV compared to ArF photons and similar, if not lower, exposure doses, the number of photons per unit area in EUV is significantly reduced. If the number of photons per contact hole is considered, the situation is even more dramatic, as the target area of a contact is smaller for EUVL than for ArF patterning. The latter argument, however, is less of a concern in the case where the contact hole is fabricated by a negative tone rather than a positive tone process. Since photon shot noise scales with 1/√(#photons), shot noise statistics would favor a brightfield negative tone over a darkfield positive tone process. Indeed, stochastic simulations predict an increase in the number of photons used to delineate a 22nm contact hole structure when printed in EUV using a negative tone instead of a positive tone process. In this paper, we will quantitatively investigate the stochastic nature of the discreet steps in the lithography process and compare the local CDU performance of contact holes for both negative and positive tone processes.
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Roel Gronheid, Gustaf Winroth, Alessandro Vaglio Pret, and Todd R. Younkin "Quantification of shot noise contributions to contact hole local CD nonuniformity", Proc. SPIE 8322, Extreme Ultraviolet (EUV) Lithography III, 83220M (22 March 2012);

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