Properties of secondary ions in ion beam sputtering of Ga2O3

Abstract

The energy distributions of secondary ions for the ion beam sputtering of a Ga2O3 target using O2+ and Ar+ ions are measured in dependence on various process parameters using energy-selective mass spectrometry. The process parameters include sputtering geometry (ion incidence angle α, polar emission angle β, scattering angle γ), the energy of incident ions Eion, and the background pressure of O2. The main secondary ion species are identified to be Ga+, O+, O2+, and, when argon is used as a process gas, Ar+. The changes in the sputtering geometry and the primary ion energy have the most impact on the energy distributions of secondary Ga+ and O+ ions, giving control over the high-energy tail, which is attributed to anisotropy effects in sputtering. The formation of O2+ ions is attributed to collisions with background gas molecules, as their energy distributions are not influenced by the sputtering geometry or the primary ion energy. The increase of the O2 pressure leads to a minor decrease of the energy of Ga+ ions due to collisions with the background gas particles. The use of primary Ar+ ions with O2 background pressure does not show any specific effect on energy distributions of Ga+, O+, and O2+ ions except for the case without additional O2 background. In the latter case, much fewer O+ and O2+ ions are produced indicative of oxygen depletion of the surface due to preferential sputtering of oxygen. At all considered O2 pressures, the energy distributions of Ar+ ions have a high-energy peak, attributed to direct scattering events. The trends in experimental data show qualitative agreement to simulations using the Monte Carlo code SDTrimSP.