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 (Vf)Vf) or substrate self-bias of −−50V. The influence of titanium precursor partial pressure on the morphology, nanostructure and optical properties was investigated. Low titanium partial pressure ([TTIP] << 0.013Pa) 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++CG] =0.027=0.027Pa and 0.093Pa were obtained. At VfVf, all the films exhibit a columnar structure, but the degree of inhomogeneity is decreased with the precursor partial pressure. Phase transformation from anatase ([TTIP] << 0.013Pa) to amorphous ([TTIP++CG] =0.093=0.093Pa) has been evidenced since the O+2+2 ion to neutral flux ratio in the plasma was decreased and more carbon contained in the film. However, in the case of −−50V, the related growth rate for different precursor partial pressures is slightly (∼∼ 15%) decreased. The columnar morphology at [TTIP] << 0.013Pa has been changed into a granular structure, but still homogeneous columns are observed for [TTIP++CG] =0.027=0.027Pa and 0.093Pa. Rutile phase has been generated at [TTIP] <0.013<0.013Pa. Ellipsometry measurements were performed on the films deposited at −−50V; results show that the precursor addition from low to high levels leads to a decrease in refractive index.
