Atomic Layer Deposition of Titanium Oxide from TiI4 and H2O2

Abstract

TiO2 thin films have been grown on amorphous soda lime glass and polycrystalline silicon substrates from TiI4 and H2O2 by atomic layer deposition (ALD) in the temperature range 250–490 °C. The film growth rate and refractive index increased linearly with growth temperature up to 300 °C. Between 300 °C and 400 °C, the film growth rate tended to stabilize. Above 400 °C, there was a further rapid increase in the growth rate, together with a corresponding increase in the thickness profile. The refractive index reached 2.70–2.75 in the films grown above 300 °C. The films contained low amounts of residual hydrogen and were virtually iodine-free. When deposited below 300 °C and above 325 °C, the films contained weakly crystallized, but still distinct, anatase and rutile phases, respectively. Reflective high-energy electron diffraction (RHEED) studies revealed that the uppermost layers of the films grown on silicon at 275 °C, 325 °C, and 425 °C contained anatase phase, regardless of deposition temperature. In the temperature range 300–325 °C, a transition region was established where either the films became less ordered, or they contained rather strongly ordered, but unstable, suboxide phases. The suboxide phase, when present, was transformed into a mixture of anatase and rutile when stored in air at room temperature.