Dual Metric OPC for Complex SRAF Implementation

Sub-Resolution Assist Feature (SRAF) insertion is one of the most important Resolution Enhancement Techniques (RET) for the 65 nm, 45 nm nodes and beyond. In this paper, we are proposing a novel approach for the optimum placement of SRAF structures using state of the art Calibre RET flow. In this approach, the optimal SRAF shapes are achieved simultaneously during the Optical Proximity Correction (OPC) stage. The main features and the SRAFs are optimized to account for their edge placement and process window metrics respectively. The resulting mask shapes deliver some of the properties that can be obtained using the Inverse Lithography Techniques (ILT), such as excellent Process Window Performance, while there is almost no impact on the runtime. The implemented model-based optimization flow remains compatible with the current OPC production flows.