On-axis radio frequency magnetron sputtering of stoichiometric BaTiO3 target: Localized re-sputtering and substrate etching during thin film growth

Abstract

BaTiO3 thin films were prepared on Nb–SrTiO3 (100) and Pt/Al2O3/SiO2/Si substrates by radio frequency (rf) magnetron sputtering using a stoichiometric BaTiO3 ceramic target. This on-axis BaTiO3 thin film growth encountered severe re-sputtering and substrate etching, above a threshold power density (4W/cm2), due to negative ion formation at the target surface and subsequent acceleration towards the substrate. However, the film deposition with reduced or negligible re-sputtering was possible below 4W/cm2 of rf-power. The rf-voltage vs. power curve showed two distinct linear regimes with high and low slopes; the change in the slope coincides with substrate etching. Optical emission spectroscopy was employed to establish the link between the onset of excessive re-sputtering and could be used as a control tool. Since, negative oxygen ions (O−) are responsible for the re-sputtering, additional processing parameters like the oxygen partial pressure [Po=(O2∕O2+Ar) %] and total pressure were also adjusted to realize target stoichiometry on the grown films. Finally, through optimization steps, as revealed by the X-ray photoelectron spectroscopy, stoichiometric BaTiO3 films were obtained, at a pressure ≥2.7Pa, power density of 2W/cm2 and Po around 50%.