Robust mask-layout and process synthesis in micro-electro-mechanical-systems (MEMS) using genetic algorithms

This thesis reports a Genetic Algorithm approach for the mask-layout and process flow synthesis problem. For a given desired target shape, an optimal mask-layout and process flow can be automatically generated using the Genetic Algorithm synthesis approach. The Genetic Algorithm manipulates and evolves a population of candidate solutions (mask-layouts and process parameters) by utilizing a process simulation tool to evaluate the performance of the candidate solutions. For the mask-layout and process flow synthesis problem, encoding schemes, selection schemes, and genetic operations have been developed to effectively explore the solution space and control the evolution and convergence of the solutions.; The synthesis approach is tested for mask-layout and process synthesis for bulk wet etching. By integrating a bulk wet etching simulation tool into the Genetic Algorithm iterations, the algorithm can automatically generate proper mask-layout and process flow which can fabricate 3-D geometry close to the desired 3-D target shape. For structures with convex comers, complex compensation structures can be synthesized by the algorithm. More importantly, the process flow can also be synthesized. For multi-step wet etching processes, proper etchant sequence and etch times for each etch step can be synthesized automatically by the algorithm. The ability to synthesize process flows makes the automatic design method more complete and more valuable.; The algorithm is further extended to achieve robust design. Since fabrication variations and modeling inaccuracy always exist, the synthesized solutions without considering these variations may not generate satisfactory results in actual fabrication. Robust design methods are developed to synthesize robust mask-layouts and process flows in “noisy” environment. Since the synthesis procedure considers the effect of variations in the fabrication procedures, the final synthesized solution will have high robustness to the variations. The robust design approaches are implemented and tested for robust mask-layout design for mask misalignment and etch rate variations. Mask-layouts robust to mask misalignment noise and etch rate variations during the fabrication can be synthesized. The synthesized mask-layouts generally improve the yield significantly by exhibiting consistent performance under a variety of fabrication conditions.