Lithographic variability and its impact on printability is a major concern in today's semiconductor manufacturing process. To address sub-wavelength printability, a number of resolution enhancement techniques (RET) have been used. While RET techniques allow printing of sub-wavelength features, the feature width itself becomes highly sensitive to process parameters, which in turn detracts from yield due to small perturbations in manufacturing parameters. Yield loss is a function of random variables such as depth-of-focus and exposure dose. In this paper, we present a first order canonical dose/focus model that takes into account both the correlated and independent randomness of the effects of lithographic variation. A novel tile-based yield estimation technique for a given layout, based on a statistical model for process variability is presented. Another novel contribution of this paper is the computation of global and local line-yield probabilities. The key issues addressed in this paper are (i) layout error modeling, (ii) avoidance of mask simulation for chip layouts, (iii) avoidance of full Monte-Carlo simulation for variational lithography modeling, (iv) building a methodology for yield estimation based on existing commercial tools. Numerical results based on our approach are shown for 45nm ISCAS85 layouts.Keywords-Photolithography, depth-of-focus, exposure dose, focus-exposure matrix (FEM), chemical mechanical polishing, stratified sampling, linewidth-based yield.

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