Relationship between Structure and Sputtering Parameters in NbN Films

Abstract

The structure of thin films of niobium nitrides was examined by reflection electron diffraction techniques. The nitride films were obtained by reactive rf sputtering of the niobium at different power levels and partial pressures of nitrogen. The films were deposited on oriented sapphire substrates maintained either at room temperature of at 400 °C. Crystal structures of three distinct phases were observed and identified as (1) α-bcc niobium with nitrogen in solid solution, (2) β-hexagonal Nb2N, and (3) δ-fcc NbN. In this study, the γ–Nb4N3 composition could not be obtained as a single phase but was always found to occur as a mixture with the δ phase. The films prepared at both high partial pressures of nitrogen and rf powers had strong textures that were dependent also on the film thickness. The electron-diffraction data showed that niobium nitride films with successive structure transformations similar to that in the bulk state can be realized and that the transformations can be correlated to the sputtering parameters used.