Reactive Ion Etching of Si Substrate using Three-Dimensional Aluminum Masks

Abstract

Three-dimensional micro fabrication process is one of the most important processes for micro-electro-mechanical systems field, optical device and many advance applications. This paper describes reactive ion etching of silicon substrates using three-dimensional aluminum masks. Aluminum masks were fabricated by photolithography, anodization and chemical etching. A 150 nm thick aluminum film was deposited on titanium-coated silicon substrates. Subsequently, square masks were patterned on the aluminum film by photolithography. After anodizing the aluminum film in 2 vol% sulfuric acid, an anodic oxide film was formed at the photoresist/aluminum film interface in addition to the open surface regions. After the anodic oxide film was removed by chemical etching in 20 vol% phosphoric acid, the resulting aluminum film surface showed convex features. Silicon substrates were fabricated using these aluminum masks. By controlling the gas mass flow and pressure, an etching rate of 32-94 nm/min and selectivity of 8.4-218 were achieved. Thus, this process proved to be effecitve method for fabricated three-dimensional microstructures on silicon substrates.