Stability and Surface Reactivity of Anatase TiO2Films

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Abstract
Atomic Layer Deposition has been used to deposit a series of TiO2 films on native oxide Si(100) at temperatures ranging from 100 to 300 °C using tetrakis(dimethylamino) titanium and H2O. The films were subjected to post-deposition thermal treatment and their structure, morphology and composition was examined. As-deposited films were amorphous and began to crystallize after thermal treatment at 500 °C. The films deposited at 100 °C and treated thermally at temperatures up to 900 °C for 10 min crystallized exclusively in the anatase phase forming crystallites with lateral size in excess of 200 nm. The films deposited at higher temperatures formed rutile crystallites with no mixing of the two phases. The films containing anatase grains exhibited significantly higher surface activity as evidenced by the detection of surface bound species such as carbonates (CO), carbon-nitrogen (CN) and nitrosyls. Although 100 °C is not within the ALD window for optimal film growth, it appears that the poor film adhesion to the substrate as well as the low film density and possibly the presence of carbon containing impurities result in the stabilization of anatase crystallites with lateral size at least one order of magnitude higher than it is widely reported in the literature.

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