Level Set Simulation of Surface Evolution in Anisotropic Wet Etching of Patterned Sapphire Subtrate

The performance of GaN-based Light Emitting Diode (LED) devices may be significantly improved by optimizing the use of maskless growth of GaN layers directly on the sidewalls of Patterned Sapphire Substrates (PSSs). In order to control the structure, arrangement, and inclination angles of the sidewalls, the use of anisotropic wet etching of sapphire needs to be clarified. To this end, this paper presents a Level Set approach to simulate the wet etching process on sapphire for the first time, thus enabling the optimization of the mask pattern for the preparation of suitable PSSs. By using the complete etch rate distribution obtained from an etched sapphire hemisphere for different concentrations and temperatures, the proposed method is expected to provide a flexible tool to determine the etched profiles of complex MEMS structures on different cuts of sapphire. In fact, the simulation results show good agreement with experiment for both transient and stable sidewalls of the trench profiles. By considering various arrays as examples, the level set algorithm is demonstrated to be applicable for simulating the fabrication of PSSs by wet etching.