Fabrication of silicon sharp nanocones using dry etch with periodic oxygen plasma shrinking and wet etch

Silicon (Si) nanocones have a wide range of applications in microelectromechanical systems and nanoelectromechanical systems. There is an increasing demand for precise control over the size and shape of nanocones. This paper proposed a novel method combining Si dry etch with periodic oxygen plasma shrinking, wet etch, and oxidation sharpening to achieve well-defined sharp Si nanocones. First, the standard Bosch process was employed to create the base part of nanocones. Second, two alternating steps of etching with sulfur hexafluoride/octafluorocyclobutane plasma and photoresist shrinkage with oxygen plasma were used to form the cone-shaped structures on top of the cylindrical bases. Third, to obtain a sharp tip, wet etching was carried out in either potassium hydroxide or a nitric acid/hydrofluoric (HF) acid mixture. To further sharpen the Si tips, thermal oxidation and HF dipping were conducted and the apex of nanocones can be down to 20 nm. This technique provides a cost-effective way to manufacture nanocones for various applications.