Sputtering characteristics, crystal structures, and transparent conductive properties of TiOxNy films deposited on α-Al2O3(0 0 0 1) and glass substrates

Abstract

Adding N2 gas during reactive sputtering of a Ti target prevented the target surface from being severely poisoned by oxygen atoms and sustained a high deposition rate for titanium oxynitride films under metal-mode-like sputtering conditions. With progress in the degree of oxidization, films deposited onto a glass substrate varied from TiO1−xNx having a face-centered cubic (fcc) structure to TiO2−xNx having an anatase structure. Titanium oxynitride films deposited on an Al2O3(0001) substrate were epitaxial with major orientations toward the (111) and (200) directions for fcc-TiO1−xNx and (112) for anatase-TiO2−xNx. Intermediately oxidized films between TiO1−xNx and TiO2−xNx were amorphous on the glass substrate but crystallized into a Magneli phase, TinO(N)2n−1, on the Al2O3(0001) substrate. Partially substituting oxygen in TiO2 with nitrogen as well as continuously irradiating the growing film surface with a Xe plasma stream preferentially formed anatase rather than rutile. However, the occupation of anion sites with enough oxygen rather than nitrogen was the required condition for anatase crystals to form. The transparent conductive properties of epitaxial TiO2−xNx films on Al2O3(0001) were superior to those of microcrystalline films on the glass substrate. Since resistivity and optical transmittance of TiOxNy films vary continuously with changing N2 flow rate, their transparent conductive properties can be controlled more easily than TiOx. Nb5+ ions could be doped as donors in TiO2−xNx anatase crystals.