Low temperature growth of nanocrystalline TiO 2 films with Ar/O 2 low-field helicon plasma

Abstract

TiO 2 thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO 2 was obtained for ion density on the substrate below 7 × 10 16 m − 3 . Increasing the ion density over 7 × 10 16 m − 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO 2. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO 2 thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.