Source Mask Optimization (SMO) is one of the most important techniques available for extending ArF immersion lithography. The combination of freeform source shape and complex mask pattern, determined by SMO, can extend the practical resolution of a lithography system. However, imaging with a small k1 factor (~0.3 or smaller) is very sensitive to many imaging parameters, such as illumination source shape error, lens aberration, process property, etc. As a result, care must be taken to insure that the source solution from SMO can be produced by the real illuminator, which is subject to its own imaging constraints. One approach is to include an illuminator simulator in the SMO loop so that only realizable illumination pupils are considered during optimization. Furthermore, the real source shape must be re-adjusted to realize expected imaging performance as may be seen, for example, in an Optical Proximity Effect (OPE) curve. In this paper we present and describe both the illuminator simulator, which can predict the real pupilgram on the exposure tool quickly, and an illumination pupilgram re-adjustment method that can effectively control the various illumination parameters to get optimum imaging performance, which is required for the lithography process design. The adjusting method uses pupilgram modulation functions, which are similar to Zernike polynomials used in wavefront aberration analysis for lithographic projection lens, to describe the optimal pupilgram adjustment, and the resulting modulation can then be realized by the illuminator system.

Date Published: 4 October 2011
PDF: 12 pages
Proc. SPIE 8171, Physical Optics, 81710L (4 October 2011); doi: 10.1117/12.899032

Published in SPIE Proceedings Vol. 8171:
Physical Optics
Daniel G. Smith; Frank Wyrowski; Andreas Erdmann, Editor(s)