Maryam Olsson

High rate reactive dc magnetron sputter deposition of Al2O3 films

Aluminum oxide films were produced by reactive dc magnetron sputtering of Al in Ar+O2. The composition of the films was characterized by Rutherford backscattering measurements. Stoichiometric films possessed excellent optical properties with a refractive index of ∼1.6 for visible and near-infrared light. It was possible to produce stoichiometric films while keeping the target in the metallic mode of operation; the resulting deposition rate was 23 nm min−1, as compared to 0.95 nm min−1 for films grown from an oxidized target. An O/Al arrival rate ratio exceeding ∼17 was required for stoichiometric films to be grown at room temperature. The success of the present high-rate deposition strategy hinges on the use of a suitable deposition system geometry — including a large target-to-substrate distance and a small target size — and on the use of sufficient Ar pressure. Monte Carlo simulations are presented; they can be reconciled with our empirical data.

Modeling of the deposition of stoichiometric Al2O3 using non-arcing dc magnetron sputtering

dc sputter deposition of stoichiometric Al2O3 is usually difficult due to the formation of an oxidized layer on the target surface, which reduces the deposition rate drastically and causes charge buildup and arcing at the target. To avoid this situation the arrival rate ratio O2/Al must be high enough at the substrate position that a stoichiometric film can form but low enough at the target that a conducting target surface is maintained. We have utilized Monte Carlo simulations to estimate the flux distribution of sputtered particles for different geometries. These results, supplemented by Bergs’ standard steady state model for the reactive sputtering process, made it possible to predict the composition at different surfaces in the processing chamber. Experimental studies were carried out for several different target-to-substrate distances and a range of sputtering gas pressures. The results show that the process can be tailored to achieve stoichiometric Al2O3 at the substrates while keeping the target in the metallic state. This is achieved by providing a high enough inert gas pressure or large enough target-to-substrate distance. Thick stoichiometric Al2O3films were successfully deposited at these conditions with low or no arcing during deposition. A considerable back-deposition of Al on to the noneroded part of the target keeping the surfaces conducting is the key factor for the reduction of arcing. (Less)