Investigation of plasma immersion ion implanted niobium oxide and titanium nitride films by nanohardness measurement

Abstract Plasma immersion ion implantation has to date mainly been used for surface and near-surface treatment of bulk material. On the other hand, it also allows for implantation into thin films. When rare gas ions are used this treatment may alter the microstructure of the films. Application of reactive ions additionally changes the composition and may lead to formation of compound phases such as oxides and nitrides. Thin films of niobium and titanium were deposited onto steel and silicon by electron beam evaporation. The films were then subjected to plasma immersion implantation. For niobium, an RF excited oxygen plasma was used. Titanium was treated with a nitrogen ECR microwave plasma. The resulting oxide and nitride films were analyzed by depth-sensing nanohardness measurements. The results were correlated with analytical findings from Rutherford backscattering and X-ray diffraction measurements. It turns out that nitrogen ion implantation into titanium yields an increase in hardness with increasing process time. By contrast, oxygen incorporation into niobium leads to a reduction in hardness which could be correlated with the oxygen content. With increasing amount of oxygen entering the film from the surface, the hardness decreases, starting from the surface and following the oxygen amount in depth. Observed hardness profile and stoichiometry profile investigated by RBS exhibit the same multilayered structure.