Fabrication of micro/nano dual-scale structures by improved deep reactive ion etching

Abstract

We present an integrated micro- and nanofabrication method to create micro/nano dual-scale silicon structures with a controllable sidewall profile over an entire 4 inch wafer. The fabrication is based on an improved Bosch deep reactive ion etching (DRIE) process and its black silicon effect, in which SF6 and C4F8 gases are used as the reactants of etching and passivation, respectively. The resultant nanostructures have apexes of <50 nm diameter, heights of 2–3 µm and an average pitch (i.e. period) of ∼400 nm. By regulating etching/passivation parameters, the black silicon effect typical in Bosch DRIE was not only controlled but also utilized to realize a sophisticated surface treatment with respect to the characteristics of liquids and optics. As a result, the optical reflectance of the nanostructured surface has been reduced to about 1% at wavelengths from 300 to 1200 nm and the contact angle of a water droplet atop the surface measured ∼160°. Moreover, by coupling this black silicon process with DRIE-based microfabrication, we have achieved various three-dimensional micro/nano dual-scale structures which show robust and stable hydrophobicity.