A robust two-step etching process for large-scale microfabricated SiO ₂ and Si₃N₄ MEMS membranes

The ability to reliably and controllably micromachine membranes by wet anisotropic etching of silicon is essential in microelectromechanical system (MEMS) device fabrication. This paper proposes an effective way to dependably microfabricate SiO₂ and Si₃N₄ membranes with little supervision. This two-step method takes full advantage of the different etching behaviors of both EDP (a solution of ethylene diamine, pyrocatechol, and water) and potassium hydroxide (KOH). First, EDP is used, which has almost no reaction with silicon nitride and a moderately fast silicon etching rate. Next, KOH is used, which has a negligible nitride etching rate and a significantly faster silicon etching rate. Using this method, fully etched membranes of large geometries can be consistently generated. The size of microfabricated membranes presented in this paper varies from 200 μm × 200 μm to 9000 μm × 9000 μm with a thickness variation from 100 nm to 1000 nm. High temperatures were used in both etchants to further increase the silicon etching rate.