Spectroscopic ellipsometry analysis of TiO2 films deposited by plasma enhanced chemical vapor deposition in oxygen/titanium tetraisopropoxide plasma

Abstract

TiO2 thin films were deposited at low pressure and temperature on silicon substrates using plasma enhanced chemical vapor deposition in oxygen rich O2/titanium tetraisopropoxide inductively coupled radiofrequency plasmas. The influence of substrate bias Vb (|Vb|≤50V) on the film properties was investigated. The results obtained by fitting ellipsometry spectra in the 1.5–6eV range, using a three-sublayer physical model, are in good agreement with the film morphology when no bias is applied or Vb=−10V. The refractive indices in the transparent range are enhanced at Vb=−50V, according to a physical model which only includes a homogenous layer and a top roughness layer. Scanning electron microscopic views show that all the films exhibit a columnar structure, but layer compactness and organization increase with the bias. The film structure evolution as a function of Vb is also evidenced on the refractive index dispersion curves. Complementary X-ray diffraction and Fourier transform infrared spectroscopy measurements show that films are basically amorphous mixed with a small amount of anatase at the floating potential (Vb=0), whereas applying a bias voltage leads to the enhancement of anatase phase and the appearance of rutile phase (Vb=−50V).