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.