Improvement of Contact OPC Model Accuracy by Using Corner Chopping

An accurate OPC model with good extrapolating capability plays an important role in achieving the accurate OPC. OPC model usually consists of physical part and empirical part which correspond to optical and resist models respectively. The optical physics has a solid theoretical foundation to follow, this part is very critical to the model accuracy and extrapolation capability. The closer the parameters (illumination, geometrical shape on real masks, etc) to real conditions are fed into optical part, the more accurate the model will be. For contact layer, the corner rounding of patterns on the real mask leads to significant deviations from original post OPC patterns. This deviation can no longer be ignored in both OPC model set up and OPC run at 32nm node and beyond. In this paper we employed a corner chopping technique to emulate the real mask shape and used it to calibrate the contact OPC model. We compared the model fitting error and extrapolate capability. The results showed the improvements in both OPC model accuracy and its extrapolation capability are significant.