Simulation work centered on double patterning processes often assumes that the problem can be approximated by considering the summation of two simple planar simulations which exhibit no interaction. Although previous work has shown that this assumption seems reasonable for interleaved line or trench patterns, it is less clear how valid it is for stitching areas where features in the two passes deliberately overlap and impinge upon each other. This work uses rigorous optical and physical resist models to study the validity of the planar summation approximation for stitching areas in a representative LELE (Litho-Etch-Litho-Etch) double line-based front end poly-silicon level process and a LELE double trench based back-end metal level process. The results suggest that the approximation holds well for back-end processes employing metal nitride type hardmask materials (which typically exhibit BARC-like optical properties). However significant deviations in behavior are observed for the poly-silicon level process suggesting that the approximation should be used with more caution on front-end processes utilizing transparent or reflective hardmask materials. It is apparent that the optical constants of both the hardmask and BARC , in addition to the tone of the double patterned feature, contribute to deviations from the approximation. Thus it is important to determine the approximation's validity on a process by process basis.

Date Published: 16 March 2009
PDF: 9 pages
Proc. SPIE 7274, Optical Microlithography XXII, 72740P (16 March 2009); doi: 10.1117/12.813566

Published in SPIE Proceedings Vol. 7274:
Optical Microlithography XXII
Harry J. Levinson; Mircea V. Dusa, Editor(s)