Effect of growth interruptions on TiO2 films deposited by plasma enhanced chemical vapour deposition

• TiO2 films deposited by plasma processes at low temperature and pressure.
• Influence of growth interruptions on structural and optical properties.
• In-situ real-time ellipsometry measurements on film properties.
• Structural and optical results are evidenced by ellipsometry analysis.

TiO2 films of ∼300 nm were deposited at low temperature (<140 °C) and pressure (0.4 Pa) using plasma enhanced chemical vapour deposition at the floating potential (Vf) or the substrate self-bias voltage (Vb) of −50 V. The impact of growth interruptions on the morphology, microstructure and optical properties of the films was investigated. The interruptions were carried out by stopping the plasma generation and gas injection once the increase of the layer thickness during each deposition step was about ∼100 nm. In one case of Vf, the films of ∼300 nm exhibit a columnar morphology consisting of a bottom dense layer, an intermediate gradient layer and a top roughness layer. But the growth interruptions result in an increase of the dense layer thickness and a decrease of surface roughness. The film inhomogeneity has been identified by the in-situ real-time evolution of the kinetic ellipsometry (KE) parameters and the modeling process of spectroscopic ellipsometry (SE). The discrepancy of the refractive index measured by SE between bottom and upper layers can be reduced by growth interruptions. In the other case of Vb = −50 V, the films exhibit a more compact arrangement which is homogeneous along the growth direction as confirmed by KE and SE. Both of Fourier transform infrared spectra and X-ray diffraction illustrate a phase transformation from anatase to rutile with the bias of −50 V, and also evidenced on the evolution of the refractive index dispersion curves. And a greatly increase of the refractive indice in the transparent range can be identified. However, the growth interruptions seem to have no influence on the morphology and optical properties in this case.