A robust pixel-based RET optimization algorithm independent of initial conditions

A robust pixel-based optimization algorithm is proposed for mask synthesis of inverse lithography technology (ILT) to improve the resolution and pattern fidelity in optical lithography. Result shows that the final image fidelity is almost independent of the initial condition. To demonstrate the robustness of the algorithm, six typical desired mask patterns and two mask technologies are applied in mask synthesis optimization using 100 randomly generated initial conditions. The critical dimension (CD) is 60nm and the partial-coherence image system is applied. It is found that the final edge placement error (EPE) and iteration number are quite weakly dependent on the initial conditions. Good final image fidelity can be acquired using arbitrary initial conditions. This algorithm is about several orders of magnitude faster and more effective than other gradient-based algorithm and simulated annealing algorithm.