Conformity and structure of titanium oxide films grown by atomic layer deposition on silicon substrates

Conformity and phase structure of atomic layer deposited TiO2 thin films grown on silicon substrates were studied. The films were grown using TiCl4 and Ti(OC2H5)4 as titanium precursors in the temperature range from 125 to 500 °C. In all cases perfect conformal growth was achieved on patterned substrates with elliptical holes of 7.5 μm depth and aspect ratio of about 1:40. Conformal growth was achieved with process parameters similar to those optimized for the growth on planar wafers. The dominant crystalline phase in the as-grown films was anatase, with some contribution from rutile at relatively higher temperatures. Annealing in the oxygen ambient resulted in (re)crystallization whereas the effect of annealing depended markedly on the precursors used in the deposition process. Compared to films grown from TiCl4, the films grown from Ti(OC2H5)4 were transformed into rutile in somewhat greater extent, whereas in terms of step coverage the films grown from Ti(OC2H5)4 remained somewhat inferior compared to the films grown from TiCl4.