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

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 SF 6 and C 4 F 8 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.