Deposition temperature dependence of titanium oxide thin films grown by remote-plasma atomic layer deposition

Abstract

Titanium dioxide (TiO2) thin films were deposited by remote-plasma atomic layer deposition (RPALD). The process window was determined in the range from 150 to 300 degrees C for atomic layer deposition of TiO2 thin film. The crystal structure and grain size of the TiO2 thin films deposited by RPALD was controlled via the variations of the deposition temperature and post-deposition thermal annealing. The as-deposited TiO2 thin film grown at 150 degrees C was amorphous whereas the TiO2 thin films grown above 200 degrees C were polycrystalline, consisting of anatase phase. As the deposition temperature increased, the grain size of the anatase phase progressively decreased. Meanwhile, when annealed at 900 degrees C, the amorphous TiO2 thin film deposited at 150 degrees C crystallized into anatase structure. The film deposited at 200 degrees C retained the anatase structure up to 900 degrees C while incurring minimal grain growth. However, the post-annealed TiO2 thin films deposited at 250 and 300 degrees C partially transformed to the rutile structure, resulting in a mixture of anatase and rutile phases. It is speculated that the relatively large grain size of the films deposited below 200 degrees C likely suppressed the anatase! rutile transformation during annealing as the reduction of total fraction of grains boundaries, which acted as primary nucleation sites for the rutile transition, delayed the anatase! rutile transformation. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim