Comparison of the characteristics of TiO₂ films prepared by low-pressure and plasma-enhanced chemical vapor deposition

Thin films of titanium dioxide (TiO₂) were deposited on silicon wafers at 450 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD), in the same reactor, using Ti(O-i-C₃H₇)₄ and oxygen as the reactants. The crystal structure, surface morphology, composition, chemical binding state and refractive index of the TiO₂ films, deposited with various r.f. powers, were characterized. Without plasma, LPCVD TiO₂ films show polycrystalline anatase structure, with a rough, granular surface and a typical refractive index of 2.43. On the contrary, the PECVD TiO₂ films are amorphous, with a smooth surface. By varying the r.f. power from 50 to 150 W, the refractive index of PECVD TiO₂ film increases with increasing power and becomes higher than 2.8 at 125 and 150 W. Despite the very different crystal structure, surface morphology and optical properties, the composition and chemical binding states of LPCVD and PECVD TiO₂ films are similar. The effect of plasma on the characteristics of CVD TiO₂ films is discussed.