Protective CVD Mullite Coatings on Single-Crystal Silicon Substrates

Abstract

Silicon has long been the primary material of choice for microelectromechanical systems (MEMS) and integrated circuit (IC) applications. However, it is prone to degradation under severe conditions such as high humidity, high temperature, and corrosive environments. To overcome such extreme conditions and help silicon perform with stability and extended lifetimes, a protection layer is proposed. Mullite (3Al2O3·2SiO2) is a known environmental barrier coating (EBC) material and has been shown to be effective on other Si-based ceramic materials. In this work, dense, high-purity crystalline mullite coatings were deposited onto single-crystal silicon substrates via chemical vapor deposition (CVD). The microstructure, orientation preference, and adhesion of these coatings were investigated. Substrate integrity in relation to the substrate/coating interface by chemical etching and coating stability in a simulated severe environment under corrosive alkali salts were investigated.