We report a study into intensity-driven mask 3D effects for N7 dark field two-bars in EUVL. For these features, traditional pupil optimization "rules" are advising to center a symmetric leaf shape illumination at the pupil plane location σY = (-0.64, 0.64). Experimentally determined critical dimension Bossungs for this exposure condition however yield an extreme best focus separation due to an additional Bossung tilt appearing at defocus values beyond 20 nm for the bottom trench. The Bossung tilts are caused by a strong coupling between the primary image of the two-bar and its first local pitch-induced self-image. The coupling to the self-image can be suppressed and, hence, the overlapping process window can be enhanced by the application of asymmetric sources, or by using standard dipole 90Y or leaf shape illuminations in combination with optimally placed sub-resolution assist features.
T. Last, P. van Adrichem, L. de Winter, S. Hsu, J. Finders, F. Wittebrood, and M. van de Kerkhof, "N7 dark field two-bar in 0.33NA EUVL: Mitigation of CD Bossung tilts caused by strong coupling between the feature's primary and 1st self-image," Proc. SPIE 10143, Extreme Ultraviolet (EUV) Lithography VIII, 1014311 (Presented at SPIE Advanced Lithography: March 01, 2017; Published: 24 March 2017); https://doi.org/10.1117/12.2257463.
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