Improvements in post-OPC data constraints for enhanced process corrections

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Current state-of-the-art OPC (optical proximity correction) for 2-dimensional features consists of optimized fragmentation followed by site simulation and subsequent iterations to adjust fragment locations and minimize edge placement error (EPE). Internal and external constraints have historically been available in production quality code to limit the movement of certain fragments, and this provides additional control for OPC. Values for these constraints are left to engineering judgment, and can be based on lithography process limitations, mask house process limitations, or mask house inspection limitations. Often times mask house inspection limitations are used to define these constraints. However, these inspection restrictions are generally more complex than the 2 degrees of freedom provided in existing standard OPC software. Ideally, the most accurate and robust OPC software would match the movement constraints to the defect inspection requirements, as this prevents over-constraining the OPC solution. This work demonstrates significantly improved 2-D OPC correction results based on matching movement constraints to inspection limitations. Improvements are demonstrated on a created array of 2D designs as well as critical level chip designs used in 45nm technology. Enhancements to OPC efficacy are proven for several types of features. Improvements in overall EPE (edge placement error) are demonstrated for several different types of structures, including mushroom type landing pads, iso crosses, and H-bar structures. Reductions in corner rounding are evident for several 2-dimensional structures, and are shown with dense print image simulations. Dense arrays (SRAM) processed with the new constraints receive better overall corrections and convergence. Furthermore, OPC and ORC (optical rules checking) simulations on full chip test sites with the advanced constraints have resulted in tighter EPE distributions, and overall improved printing to target.