Investigation of Anisotropic Etching Characteristics of Si{110} in IPA-Added NH 4 OH Etchant for MEMS Applications

This study investigates the wet anisotropic etching behavior of Si{110} wafers in ammonium hydroxide (NH₄OH), with and without the addition of isopropyl alcohol (IPA), as etchants for MEMS applications involving the formation of various microstructures. A SiO2 thin film is employed as the masking layer, and photolithography is used to transfer microstructure patterns onto the SiO₂. The concentration of IPA is varied incrementally from 2% to 20%, while the NH₄OH concentration remains fixed at 70°C. The study reveals that pure NH₄OH yields high etch rates, pronounced undercutting at convex corners, and increased surface roughness. In contrast, the incorporation of IPA significantly suppresses these effects, leading to smoother etched surfaces and enhanced dimensional control. These findings demonstrate the potential of IPA-added NH₄OH solutions as effective etchants for accurately fabricating microstructures with smooth surfaces, making them well-suited to a range of MEMS-based sensor applications.