Diaphragm Thickness Control in Silicon Pressure Sensors Using an Anodic Oxidation Etch‐Stop

Abstract

An etch‐stop technique for silicon diaphragm formation has been developed. In the experiment, n/p epitaxial silicon wafers were used. The wafer was immersed in a hydrazine/water solution and a positive voltage was applied to an n‐type epitaxial layer. After the thick p‐type substrate was etched off, silicon etching was automatically stopped, and only a thin n‐type epitaxial layer diaphragm was left. The etch‐stop mechanism is considered to be as follows: after the p‐type substrate is chemically etched off, an oxide film is formed by an anodic oxidation process on the n‐type layer surface. The oxide film protects the n‐type silicon from being etched by the hydrazine/water solution. Piezoresistive silicon diaphragm pressure sensors with precise diaphragm thickness have been fabricated using this etch‐stop technique. Diaphragm thickness was controlled to .