Step flow-based cellular automaton for the simulation of anisotropic etching of complex MEMS structures

An enhanced octree data representation is developed for use in atomistic simulations of the evolution of complex multivalued surfaces appearing during anisotropic etching of crystalline silicon in micro electro mechanical systems (MEMS) applications. The octree provides a good balance between accuracy, memory efficiency and calculation speed. In combination with the octree, a step flow-based cellular automaton (CA) model is considered, which can be used to convert the experimental macroscopic etch rates into atomistic removal rates for direct use in the simulations. This involves minimizing the global error between the experimental values and the non-linear analytical expressions of the etch rates for a small set of chosen orientations. The orientations where the etch rate suffers a sudden change against the cutting angle play a crucial role to generate an optimal solution. The simulated etch rates for KOH and KOH/IPA systems in different concentrations show good agreement with the experiments. Due to the improved description of the anisotropy, the propagation of the etch front in realistic engineering applications can be simulated accurately.