For the three-dimensional (3-D) numerical study of photoresist etching processes, the 2-D dynamic cellular automata (CA) model has been successfully extended to a 3-D dynamic CA model. Only the boundary cells will be processed in the 3-D dynamic CA model and the structure of "if-else" description in the simulation program is avoided to speed up the simulation. The 3-D dynamic CA model has found to be stable, fast and accurate for the numerical study of photoresist etching processes. The

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... simulation, post-exposure bake (PEB) simulation and etching simulation are integrated together to further investigate the performances of the CA model. Simulation results have been compared with the available experimental results and the simulations show good agreement with the available experiments. cellular automata, process simulation, optical lithography simulation, model As the micro-electro-mechanical systems (MEMS) design and fabrication become increasingly advanced, accurate three-dimensional (3-D) simulation systems for fabrication processes such as etching, lithography, deposition processes, etc. demonstrate to be useful to improve the efficiency of MEMS design and to reduce the development costs of MEMS products. At the same time, 3-D optical lithography simulation becomes significantly important for the accurate analysis of complex structures, such as contacts, corners, etc., and for the optimization of the masks for these structures, as the complexity of integrated circuits (IC) increases [1] . Furthermore, simulation is essential to determine the best way of pushing the present set of equipment involved in optical lithography to its maximum limits [2] . The photoresist etching simulation is usually the most time-consuming step among the basic optical lithography simulation steps [3] , so the key to increase the speed of optical lithography simulation is to speed up the simulation of the photoresist etching process. During the past two decades, some simulators for optical lithography processes have been successfully developed