## Abstract

Illumination source optimization (SO) in optical lithography is generally performed under a simulation model that does not consider critical effects such as the vectorial nature of light and mask topography. When a numerical aperture becomes large and the critical dimension reaches subwavelength, the prediction of this model generally fails; therefore, the previous works based on this model become inaccurate. In order to correctly compute SO, we first propose a new source pattern representation method that has moderate parameter variations but remains complete in solution space. Then we develop a derivative-free optimization (DFO) method to optimize these parameters under a rigorous simulation model. Unlike gradient-based techniques, DFO methods do not require a closed-form formulation of the model and are independent of the form of cost function.

© 2014 Optical Society of America

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