Fabrication of High Aspect Ratio Silicon Nanostructure with Sphere Lithography and Metal-Assisted Chemical Etching and its Wettability

Int. J. of Automation Technology submitted 1 Metal-assisted chemical etching (MACE) is site-selective etching process due to catalyst reaction at the interface between noble metal and silicon. This paper aims to make clear the applicability of sphere lithography and MACE to fabricate high aspect ratio Si nanostructures. The capacity to control the etched profiles and scale extension were investigated. Firstly, silica particles (e.g. 1 μm) were self-assembled on a Si substrate. After the reduction of particle size by argon ion bombardment, a gold layer was deposited using the particles as a mask. The substrate was then etched with mixture of hydrofluoric acid and hydrogen peroxide. It was found that an array of nanopillars was produced with regular pitch, good separation and aspect ratio reached about 52. Effect of MACE conditions on final profiles was made clear. Limitation of this approach is small range of fabricated area (several millimeters) due to the dependence on vacuum technique (ion bombardment, Au deposition) which limited its practical applications. Thus Ag nanoparticle (e.g. 150 nm) was applied. Relationship between concentration of Ag suspension, Ag assembled layer and morphology of MACE structures was made clear. Spray method was applied to extend deposited area of Ag particles up to 100 mm. Finally, effect of cross-sectional profile on the contact angle of water droplet was examined. By applying high aspect ratio nanostructure on the substrate, the water contact angle increased up to 153 degrees while that without structure was 58 degrees.