Study of TiO₂ film growth mechanisms in low-pressure plasma by in situ real-time spectroscopic ellipsometry

We investigate the initial stages of growth of TiO₂ films prepared by plasma-enhanced chemical vapor deposition on plasma pre-oxidized c-Si, using in situ real-time spectroscopic ellipsometry. The optical properties of TiO₂ films were parameterized from 245 to 1000 nm using the Tauc-Lorentz oscillator and the effective medium approximation. For thin films grown at low substrate temperature (T_s = 75 °C) and deposition rate (0.3<r<3.5 Å/s), effective refractive index (n ₅₅₀ at λ = 550 nm) stabilization, consistent with island coalescence, was observed for thickness, d, of only 12-15 Å, independent of r. When compared at final thickness (d∼85 Å), all films possessed similar optical properties in the visible (n₅₅₀ = 2.30-2.33), with most significant differences in n(λ) and k(λ) observed in the interband region (λ<385 nm). A thicker film (d = 700 Å) grown at r = 3.5 Å/s was found to exhibit similar growth behavior for d<85 Å. An additional n₅₅₀ increase in the order of 0.03 observed for 85<d<280 Å, was attributed to refractive index inhomogeneity.