Influence of water contamination on the sputtering of silicon with low energy argon ions investigated by Molecular Dynamics simulations.

Abstract

Focused ion beams (FIB) are a common tool in nanotechnology for surface analysis, sample preparation for electron microscopy and atom probe tomography, surface patterning, nanolithography, nanomachining and nanoprinting. For many of these applications, a precise control of the ion-beam induced processes is essential. The effect of contaminations on these processes has not been explored thoroughly but can often be substantial, especially for ultralow impact energies in the sub-keV range. In this paper we investigate by molecular dynamics (MD) simulations how one of the most commonly found residual contaminations in vacuum chambers, i.e. water, adsorbed on a silicon surface, influences sputtering by 100 eV argon ions. The incidence angle was changed from normal incidence close to grazing incidence. For the simulation conditions used in this work, the adsorption of water favours the formation of defects in silicon by mixing of the hydrogen and oxygen atoms into the substrate. The sputtering yield of silicon is not changed significantly by the contamination, but the fraction of hydrogen and oxygen atoms that is sputtered depends largely on the incidence angle. This fraction is largest for incidence angles between 70 and 80 degrees defined with respect to the sample surface. Overall, it changes from 25% to 65%.