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 ion-beam-induced processes is essential. The effect of contaminations on these processes has not been thoroughly explored 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 to 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 hydrogen and oxygen atoms into the substrate. The sputtering yield of silicon is not significantly changed by the contamination, but the fraction of hydrogen and oxygen atoms that is sputtered largely depends on the incidence angle. This fraction is the largest for incidence angles between 70 and 80° defined with respect to the sample surface. Overall, it changes from 25% to 65%.

Ultralow-energy amorphization of contaminated silicon samples investigated by molecular dynamics

“…The force fields used to simulate the Ar bombardment of a contaminated silicon sample have already been described in a previous article [ 26 ]. To summarize, they are composed of a set of two interatomic potentials.…”

“…Typical contaminations are (in the order of frequency) water, nitrogen, carbon and carbonated components that can be found in the atmosphere [ 22 – 24 ], and residuals from past experiments in the chamber, which can include silicon, carbon, or any type of particles that were sputtered previously and adsorbed on the walls of the sample chamber [ 24 – 25 ]. The work in this paper will be based on methodologies developed in a previous paper [ 26 ], which focused on a silicon sample contaminated with a water layer, and in which we showed the influence of the contamination layer on the sputtering process. In the presence of water on the sample surface, we showed that while the amorphization depth was substantially increased, there was no significant impact on the silicon sputtering yield.…”

Ultra-low energy amorphization of contaminated silicon samples investigated by Molecular Dynamics

“…On the other hand, the simplicity of the Morse potential allowed us to represent the interactions between the full valence band argons atoms and the sample atoms. As described in previous work [26], a set of DFT calculations were performed using VASP to compute the Morse potential for argonsilicon, argonhydrogen and argonoxygen interactions.…”

“…By increasing the number of ion impacts, a higher fluence is reached, e.g 500 ion bombardments on a surface of 18.9 nm² results in a fluence of 2.6 x 10 15 atoms/cm². A more in-depth description of the full preparation of the sample and the workflow for continuous ion bombardment is given in a previous publication [26].…”

“…Typical contaminations are (by order of frequency): water, nitrogen, carbon and carbonated components that can be found in the atmosphere [22][23][24], residuals coming from past experiments in the chamber, which can include silicon, carbon, or any type of particles that would have been sputtered previously and adsorbed on the walls of the sample chamber [24,25]. The work in this paper, will be based on methodologies developed in a previous paper [26], which focused on a silicon sample contaminated with a water layer and in which we showed the influence of the contamination layer on the sputtering process. With the presence of water on the sample surface, we showed that while the amorphization 4 depth was substantially increased, the silicon sputtering yield was not impacted significantly.…”