KOH etching process of perfect square MEMS corrugated diaphragm

摘要

In this paper, silicon corrugated diaphragms with non-compensated and compensated mask layout have been fabricated on a single silicon (100) wafer by using potassium hydroxide (KOH) etching technique. Although, recently corrugated diaphragms have been used for a diaphragm structure due to its excellent properties, no theoretical and analytical studies on the fabrication process of these diaphragms have been performed. Therefore, the characterization of the KOH etching process with emphasized on convex corner behavior has been studied through both experiments and simulations in order to realize the perfect corrugated diaphragm. Details of the etching of corrugated diaphragms have been studied by using process simulation software of a three-dimensional anisotropic etching profile prior to fabrication process. The influence of the KOH etching temperature and concentration on the convex corner undercutting of corrugated diaphragm are observed. The convex corner behavior has been analyzed based on the geometrical parameters and the new emergent high index silicon planes. It was found that the convex corner undercutting phenomena is significantly reduced at low etching temperature and high KOH concentration respectively. It can be concluded that the prominent facets contributing to the undercutting of the convex corners of the corrugated diaphragm for the given etching condition coincide with the {411} plane. The introduction of the additional mask layout for the protection of convex corners at all convex-mask geometry of the corrugated diaphragm during the KOH etching process has been proved by simulation to produce almost perfect square corners. These simulation results have been confirmed by experiments.