Growth of crystalline alumina and titanium-oxynitride thin films by metalorganic chemical vapor deposition

Crystalline Al₂O₃ films and Ti-oxynitride (TiO _xN_y) films have been deposited by metalorganic chemical vapor deposition (MOCVD). These films were developed for potential use as wear-resistant coatings for cutting tools. Aluminum acetylacetonate was used as the precursor material for the deposition of Al₂O₃ films. Mostly amorphous film was deposited below 750°C. With increase in deposition temperature, crystallinity of the film increased—a strong ⟨011⟩ textured κ-Al ₂O₃ film was deposited at 950°C. In the absence of water vapor, the Al₂O₃ film growth rate increased with increase in temperature whereas in the presence of water vapor, the growth rate was higher and decreased with increase in temperature. TiO_xN_y film with isomorphous TiN structure was deposited using titanium tetraisopropoxide and NH₃. XRD analysis of the film deposited on Si(111) and mica substrates at 600°C revealed a (111) TiO_xN_y peak and TiO₂ (rutile) peaks. At low temperatures, below 600°C, the deposited films contained only TiO₂ (anatase) phase. At 650°C and above, both anatase and rutile TiO₂ phases were present. The film growth and morphology depended on precursor, NH₃ and diluent gas flow rates. The optimum bubbler and NH₃ flow rates under the given processing conditions were about 300–350 sccm. Increase in NH ₃ flow at a constant precursor flow resulted in smaller angular clusters, and dilution of the inlet stream resulted in a higher growth rate and an increase in cluster size and angularity. A machining test confirmed that a TiO _xN_y coated tool insert performs better than an uncoated tool insert. During the MOCVD of TiO_xN_y films, growth of TiO₂ nanorods on a WC-Co substrate at 500°C was discovered. The presence of cobalt on the substrate surface catalyzes the nanorod growth. In a separate study, classical and atomic nucleation theories were used to calculate the nucleation rates of hypothetical Ag deposition on W substrate at various process conditions. It was found that for practical deposition conditions, both theories are equally useful for nucleation rate studies.