Nanoscale Surface Patterning of Silicon Using Local Swelling Induced by He Implantation through NSL-Masks

A novel technique to form periodically nanostructured Si surface morphologies based on nanosphere lithography (NSL) and He ion implantation induced swelling is studied in detail. It is shown that by implantation of keV He ions through the nanometric openings of NSL masks regular arrays of hillocks and rings can be created on silicon surfaces. The shape and size of these surface features can be easily controlled by adjusting the ion dose and energy as well as the mask size. Feature heights of more than 100 nm can be obtained, while feature distances are typically 1.15 or 2 (hillock or ring) nanosphere radii, which are chosen to be between 100 and 500 nm in this study. Atomic force and scanning electron microscopy measurements of the surface morphology are supplemented by cross-sectional transmission electron microscopy, revealing the inner structure of hillocks to consist of a central cavity surrounded by a hierarchical arrangement of smaller voids. The surface morphologies developed here have the potential to be useful for fixing and separating nano-objects on a silicon surface.