Controlling the crystallinity and roughness of atomic layer deposited titanium dioxide films

The surface roughness of thin films is an important parameter related to the sticking behaviour of surfaces in the manufacturing of microelectomechanical systems (MEMS). In this work, TiO₂ films made by atomic layer deposition (ALD) with the TiCl₄–H₂O process were characterized for their growth, roughness and crystallinity as function of deposition temperature (110–300 °C), film thickness (up to ∼100 nm) and substrate (thermal SiO₂, RCA-cleaned Si, Al₂O₃). TiO₂ films got rougher with increasing film thickness and to some extent with increasing deposition temperature. The substrate drastically influenced the crystallization behaviour of the film: for films of about 20 nm thickness, on thermal SiO₂ and RCA-cleaned Si, anatase TiO₂ crystal diameter was about 40 nm, while on Al₂O₃ surface the diameter was about a micrometer. The roughness could be controlled from 0.2 nm up to several nanometers, which makes the TiO₂ films candidates for adhesion engineering in MEMS.