Deep Wet Etching in Hydrofluoric Acid, Nitric Acid, and Acetic Acid of Cavities in a Silicon Wafer

Abstract

This paper reports an experimental investigation of deep isotropic etching in HF:HNO3:CH3COOH solution for the fabrication of large microcavities in a silicon wafer. The effects of different practical parameters, e.g., back protective layer, etch window diameter and agitation method, are evaluated experimentally and then discussed. Results show that, for the conditions used, the back protective layer has little influence on the etched depth. Experimental etched profiles are in agreement with the mathematical model of Kuiken's assuming a purely diffusion-controlled etching. Vertical anisotropy and asymmetry of etched profiles were observed. A 100 µm deep hemispherical microcavity was obtained for a 60 min etching with magnetic agitation at room temperature.