Accounting for mask topography effects in source-mask optimization for advanced nodes

We present a comprehensive study of applicability of a fast 3D mask model in the context of source-mask optimization to advanced nodes. We compare the results of source optimization (SO) and source-mask optimization (SMO) with and without incorporating a fast 3D mask model to the rigorous 3D mask simulations and wafer data at 22 nm technology node. We do this comparison in terms of process metrics such as depth of focus (DOF), exposure latitude (EL), and mask error enhancement factor (MEEF). We try to answer the question of how much the illumination shape changes with the introduction of mask topography effect. We also investigate if the illumination change introduces any mask complexity and at which level. Correlation between MEEF and any mask complexity due to source variation is also explored. We validate our simulation predictions with experimental data.