Annealing and Characterization of Niobium Oxide Films Deposited With Atomic Layer Deposition

Niobium oxides have seen a rise in interest due to their potential usefulness in optical, electronic, and memristive devices. Specifically, Nb₂O₅ and NbO₂ have bandgaps of ~3.5 eV and ~1.2 eV, respectively. Nb₂O₅ is a high-k dielectric (k~41) and has a high refractive index (n~2.2). Both materials have the potential to be used in nonvolatile or volatile memristor devices. Amorphous thin-films of Nb₂O₅ and NbO₂ were grown with atomic layer deposition on 4” Si(110) wafers with native oxide. The wafers were diced into 1 cm squares, and annealed in both inert and reducing environments in an atmospheric pressure tube furnace. The anneals were performed for up to 120 minutes, with temperatures ranging from 550 ^○C up to 1000 ^○C. It was found with X-ray diffraction and Raman spectroscopy that the amorphous Nb₂O₅ crystallizes at 550 ^○C, and nucleates crystalline NbO₂ islands at 750 ^○C. Anneals performed at 1000 ^○C were found to be fully recrystallized as NbO₂. As-deposited amorphous NbO₂ was found to crystallize at similar temperatures. For both NbO₂ and Nb₂O₅, trends were observed in the sample morphology, indicating that annealing temperature and duration are important in the reduction and recrystallization of as-grown Nb₂O₅ and NbO₂ on SiO₂.