Group V transition metal-based mixed nitrides formed by nanoscale reactive ion beam mixing of interfaces

Nb- and Ta-based mixed nitrides have been grown by 3 keV N2+ nanoscale reactive ion beam mixing (IBM) of Nb/Si and Ta/Al interfaces. The kinetics of growth, composition and electronic structure of the films formed has been studied using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). A similar reactive IBM kinetics of three stages has been found for both interfaces by means of factor analysis. In a first stage, a mixture of substoichiometric and stoichiometric nitride species are formed up to ion doses of ~ 1.5 × 1016 ions/cm2. In a second stage, for ion doses up to ~ 5–6 × 1016 ions/cm2, subtoichiometric nitride species are completely transformed into stoichiometric nitride species. Subsequently, in a third stage, stoichiometric nitride species are transformed progressively into mixed nitride species due to the strong intermixing taking place at the interfaces, in such a way that a transition from metallic to insulator behaviour is observed in the UPS valence band. This transformation is accompanied by changes in the nitrogen concentration and a decrease of the Nb/Si or Ta/Al ratio in the thin mixed nitride films formed leading to the synthesis of custom designed group V transition metal-based mixed nitrides. Angle resolved XPS shows that the composition of the films formed by reactive IBM is rather uniform in the near-surface region. Experimental results have been compared with Monte Carlo TRIDYN simulations, suggesting that, in addition to pure ballistic mechanisms, radiation enhanced diffusion effects and the reaction with nitrogen should be also taken into account to explain the reactive IBM of Nb/Si and Ta/Al interfaces.