Considering MEEF in inverse lithography technology (ILT) and source mask optimization (SMO)

Mask Error Enhancement Factor (MEEF) plays an increasingly important role in the DFM and RET flow required to continue shrinking designs in the low-k1 lithography regime. The ability to model and minimize MEEF during lithography optimization and RET application is essential to obtain a usable process window (PW). In Inverse Lithography Technology (ILT), MEEF can be included in the cost function as a nonlinear factor, so that the inversion minimizes MEEF, in addition to optimizing PW and edge placement error (EPE). ILT has been shown to optimize masks for a given source. Using ILT for contemporaneous Source and Mask co-Optimization (SMO) can provide further benefit by balancing the complexity of mask and source. Results demonstrating the benefits of "MEEF-aware" ILT and SMO for advanced technology nodes are presented in this paper.