Fabrication of ultra-high-aspect-ratio nano-walls and nano-structures on silicon substrates

Realization of high-aspect-ratio vertical features on silicon substrates is a crucial step in the fabrication process of microelectromechanical systems devices. Therefore deep reactive ion etching (DRIE) plays an important role in the fabrication of those structures. Recently many efforts have been made in order to propose the novel DRIE processes in order to achieve higher aspect ratios; however, they suffer from complexity and high sensitivity to process parameters. Herein, the authors report a high-aspect-ratio vertical etching of silicon by employment of proposed low temperature SiO2 deposition on Si substrate, using of H-2 and O-2 gases. The process employs multiple sequences of alternating steps of etching by a fluorine donating gas such as SF6 and sidewall passivation by SiO2. Etch rates reach up to 0.8 mu m min(-1) and values of aspect ratio higher than 100 are readily achievable by this process. Furthermore, this process also allows for controlled fabrication of nano-wall and high-aspect-ratio nano-wall tube as well as three-dimensional silicon structures.