Design of automatic controllers for model-based OPC with optimal resist threshold determination for improving correction convergence

Model-based Optical Proximity Correction (MBOPC) has become one of the most important resolution enhancement technologies (RETs), which can effectively improve the image fidelity and process robustness. MBOPC is performed by iteratively shifting the polygon edges of mask patterns until convergence requirements are achieved. In this paper, we specifically discuss the design of feedback controllers to improve MBOPC convergence. Effective controller design rules are derived from the OPC results of several circuit layouts. Meanwhile, resist models also significantly affect MBOPC convergence. Two kinds of resist model have been proposed for MBOPC such as constant threshold resist model (CTRM) and variable threshold resist model (VTRM). We propose a novel CTRM, called pattern-based optimal threshold determination (PBOTD). By normalized mean square error (NMSE) formulation, appropriate threshold values with minimum NMSE can be determined to improve image fidelity, and effectively decrease iterations required. The effectiveness of applying both optimized controller and PBOTD is demonstrated on a 90-nm SRAM cell.