Structural and optical properties of RF-biased PECVD TiO2 thin films deposited in an O2/TTIP helicon reactor

•Development of TiO2 film growing morphology at the floating potential.•Biasing effect on the evolution of O/Ti ratio and binding energy shift.•Decrease of optical bandgap energy with substrate bias.•Spectroscopic ellipsometry fitting process on the optical properties.•Comparison of optical index between thin film and bottom layer of thick film.

TiO2 thin films are deposited from oxygen/titanium tetraisopropoxide inductively coupled radiofrequency plasmas at low temperature and pressure by a RF-biased PECVD technique. In such a process, the substrate biasing effect (Vb) on the related film composition, structure, morphology, and optical properties are investigated. The results show that the O:Ti concentration ratio in all the films is roughly in stoichiometric proportion of 2, and the binding energy difference between the O 1s and Ti 2p3/2 levels indicates the formal valence state Ti4+ in all the films. The phase transformation from anatase to rutile is identified by Raman spectroscopy. At the floating potential, the first growth stage yields a well organized columnar layer, ∼90 nm in thickness, and this layer within a thick film (∼365 nm) has roughly the same optical properties as the thin film of ∼90 nm which is separately deposited. However, the columnar structure can be eliminated by using |Vb| ≧ 50 V. Spectroscopic ellipsometry is used to obtain the film optical properties, and appropriate fitting parameters have been found for the measured data.