The Effect of Plasma Gas Composition on the Nanostructures and Optical Properties of TiO2 Films Prepared by Helicon-PECVD

Abstract

TiO2 films were deposited from oxygen/titanium tetraisopropoxide (TTIP) plasmas at low temperature by Helicon-PECVD at floating potential ([Formula: see text] or substrate self-bias of [Formula: see text]50[Formula: see text]V. The influence of titanium precursor partial pressure on the morphology, nanostructure and optical properties was investigated. Low titanium partial pressure ([TTIP] [Formula: see text] 0.013[Formula: see text]Pa) was applied by controlling the TTIP flow rate which is introduced by its own vapor pressure, whereas higher titanium partial pressure was formed through increasing the flow rate by using a carrier gas (CG). Then the precursor partial pressures [TTIP[Formula: see text]CG] [Formula: see text][Formula: see text]Pa and 0.093[Formula: see text]Pa were obtained. At [Formula: see text], all the films exhibit a columnar structure, but the degree of inhomogeneity is decreased with the precursor partial pressure. Phase transformation from anatase ([TTIP] [Formula: see text] 0.013[Formula: see text]Pa) to amorphous ([TTIP[Formula: see text]CG] [Formula: see text][Formula: see text]Pa) has been evidenced since the O[Formula: see text] ion to neutral flux ratio in the plasma was decreased and more carbon contained in the film. However, in the case of [Formula: see text]50[Formula: see text]V, the related growth rate for different precursor partial pressures is slightly ([Formula: see text] 15%) decreased. The columnar morphology at [TTIP] [Formula: see text] 0.013[Formula: see text]Pa has been changed into a granular structure, but still homogeneous columns are observed for [TTIP[Formula: see text]CG] [Formula: see text][Formula: see text]Pa and 0.093[Formula: see text]Pa. Rutile phase has been generated at [TTIP] [Formula: see text][Formula: see text]Pa. Ellipsometry measurements were performed on the films deposited at [Formula: see text]50[Formula: see text]V; results show that the precursor addition from low to high levels leads to a decrease in refractive index.