Dry etching of diamond nanowires using self-organized metal droplet masks

Abstract

In a top–down approach diamond nanowires (DNW) were fabricated by anisotropic oxygen plasma etching of undoped or boron doped polycrystalline diamond layers. Dewetting an evaporated metal film, resulting in randomly distributed metal droplets of 5–50 nm in diameter, created the etching mask. This study focused on the investigation of the effect of the metal layer type, i.e., Al, Ti, Co, Ni, Cu, Pd, Pt and Au, and thickness on surface density, shape and size of the resulting droplets. Two dry etching techniques were studied: (1) Capacitively Coupled Plasma Reactive Ion Etching (CCP-RIE) and (2) Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). Using CCP-RIE diamond etch rates were between 10 nm/min and 50 nm/min; however, diamond/Ni selectivity was not high enough to fabricate nanowires > longer than 250 nm. ICP-RIE etching created tapered, high aspect diamond nanostructures at 1000 W plasma power, 10 W platen power for ion acceleration and long etching times (> 40 min) while preserving the mask. Anisotropy can be improved by the addition of Ar in the plasma and the reduction of the pressure. So far, vertically aligned diamond nanowires of 800 nm in length were obtained by ICP-RIE etching in appropriate conditions.