Metal-assisted chemical etching of silicon with deposited Ag nanoparticles aiming for functional surfaces

摘要

Metal-assisted chemical etching is one of the anisotropic etching processes of silicon. The major characteristic is site-selective process due to catalytic reaction at the contact point between noble metal and silicon, and a high-aspect ratio can be obtained. This paper aims to make clear the possibility of the metal nanoparticle deposition and its effect on the etched profiles including an application to the production of hydrophobic surfaces. Suspension that contains silver-nanoparticles was dropped on a silicon substrate. By changing the particle concentration, the coverage of the particles could be controlled. Then, the effect of etchant condition, mixture of fluoric acid and hydrogen peroxide water, on the etching rate and final profile was made clear. It was found that an array of nanopores or nanopillars were produced and the aspect ratio reached about 40. Since steep cross-sectional profile can change the wettability of the surface, its effect on the contact angle of water droplet was examined. By applying nanostructure on the substrate, the contact angle increased up to 126 degrees while that without structure was 58 degrees.