Mechanical properties and structure of TiO2 films deposited on quartz and silicon substrates

Abstract

TiO2 films were deposited by reactive direct current magnetron sputtering on conductive and semiconductive Si as well as on dielectric quartz substrates at different negative substrate biases generated by radio-frequency (RF) power applied to the substrate holder. The mechanical properties of the films (depth sensing indentation) were examined in dependence on the film structure (X-ray diffraction and Raman spectroscopy).Hard rutile phase grows at negative substrate bias higher than 90V, while softer anatase phase at ground or low bias (≤50V) irrespective of substrate electrical conductivity. Phase composition (rutile, anatase or their mixture) as well as corresponding hardness and elastic modulus values strongly depend on electrical conductivity of the substrate at medium biases (~50–75V).Phase analysis and hardness data imply that RF induced self-bias on the upper surface of quartz substrate is smaller in comparison to that on the surface of the semiconductive and especially conductive Si substrate. The rutile phase still grows after the RF power is switched off. The rutile grain size increases while hardness decreases in this case. Micro-Raman spectroscopy of residual indents in the films with anatase structure points out on the more dense high pressure TiO2-II structure formed during the indentation.