The effect of the backscattered energetic atoms on the stress generation and the surface morphology of reactively sputtered vanadium nitride films

During the reactive magnetron sputtering of transition metal nitrides in an Ar–N2 ambient, Ar+ and N2+ plasma ions are neutralized upon impingement on the target and are backscattered towards the growing film as neutral Ar and N species, respectively. Based on simulations, as well as on plasma and on film characterization techniques we manifest the relationship between the bombardment by the backscattered energetic atoms and the properties of reactively sputtered vanadium nitride (VN) films. Depending on the N2 flow (qN2) two bombardment regimes are established. In the first regime, (qN2<20 sccm) the contribution of the N species to the energetic bombardment is insignificant. The major bombarding species in this regime are the backscattered Ar species, as well as positive plasma ions and sputtered atoms. These species have relatively low energies and subplantation ratios and thus, their energy is transferred to the surface of the growing film. In the second regime (qN2>20 sccm) the backscattered N atoms are the major bombarding species and their flux to the growing film increases with increasing the N2 flow. We argue that the backscattered N atoms have higher energy and subplantation ratio in comparison to the other bombarding species. As a result, a higher part of their energy is dissipated in the bulk of the film. The two bombarding regimes correlate well with the residual compressive stresses and the surface roughness of the films. Films grown at qN2<20 sccm exhibit low compressive stresses and their roughness drops when qN2 is increased. This consistent with the low subplantation ratio and the transfer of the energy of the bombarding species to surface the growing film. The compressive stresses of films grown at qN2>20 sccm are higher, than those of the films grown in the first regime, and increase with increasing N2 flow. This is attributed to the subplantation of the bombarding N species in the growing film.