Layer sub-patterns with exclusive SMO
Mixtures of different sub-pattern layouts at different locations with different optimized (pupil) sources can occur in the same layer, as expected for random logic BEOL layers with same minimum pitch. That could mean EUV needs multi-patterning due to the need for separate optimized pupils. Some recent published examples are listed below.
The effect of multiple included layer sub-patterns in SMO was demonstrated in a paper from SPIE 2017 (W. Gillijns et al., reference below). Here the anchor pitch is 32 nm while the overlay mark is a 200 nm pitch 100 nm feature; it already took some optimization to get them together with the 2-bar in the same focus window without shifting more than 0.8 nm. However, including more sub-pattern clips from the same layer into the optimization resulted in some sub-patterns shifting up to 1 nm in the same focus window.
More recently, ASML/IMEC/TEL showed in an SPIE Photomask 2018 paper (D. Rio et al., reference below) that SMO was more effective in addressing tip-to-tip printability with a lower illumination efficiency of the pupil (i.e., more light is discarded, due to lower pupil fill). Despite this tip-to-tip improvement, the SMO with a weighted optimization for line-space gratings and tip-to-tip gratings only did not improve printability for non-grating parts of a 32 nm pitch logic clip, e.g., where one side of the dense trench is a gap.
References:
J. Mulkens, J. Karssenberg, H. Wei, M. Beckers, L. Verstappen, S. Hsu, and G. Chen,
"Across Scanner Platform Optimization to enable EUV Lithography at the 10-nm Logic Node," Proc. SPIE vol. 9048, 90481L (c) 2014 SPIE.
X. Liu, R. Howell, S. Hsu, K. Yang, K. Gronlund, F. Driessen, H-Y. Liu, S. Hansen, K. van Ingen Schenau, T. Hollink, P. van Adrichem, K. Troost, J. Zimmermann, O. Schumann, C. Hennerkes, and P. Graupner,
"EUV source-mask optimization for 7 nm node and beyond," Proc. SPIE vol. 9048, 90480Q (c) 2014 SPIE.
C. Tabery, J. Ye, Y. Zou, V. Arnoux, P. Raghavan, R-H. Kim, M. Cote, L. Mattii, Y-C. Lai, and P. Hurat,
"In-design and signoff lithography physical analysis for 7/5nm," Proc. SPIE vol. 10147, 1014705 (c) 2017 SPIE.
W. Gillijns, L. E. Tan, Y. Drissi, V. Blanco, D. Trivkovic, R. H. Kim, E. Gallagher, and G. McIntyre,
"Reticle enhancement techniques towards iN7 Metal2," Proc. SPIE vol. 10143, 1014314 (c) 2017 SPIE.
D. Rio, V. Blanco, J.-H. Franke, W. Gillijns, M. Dusa, E. De Poortere, P. Van Adrichem, K. Lyakhova, C. Spence, E. Hendrickx, S. Biesmans, K. Nafus,
"EUV pupil optimizations for 32nm pitch logic structures," Proc. SPIE vol. 10809, 108090N (c) 2018 SPIE.