In situ investigation of magnetron sputtering plasma used for the deposition of multiferroic BiFeO₃ thin films

Somrani et al. (J. Mater. Sci. 26:3316–3323, 2015) have recently investigated the BiFeO₃ (BFO) thin films growth by RF magnetron sputtering. The role of the processing parameters especially the oxygen flow, deposition temperature and annealing on the microstructure and optical properties of the deposited films has been extensively studied. In this work a detailed investigation of the plasma deposition dynamics of BFO films is presented. A plasma sampling mass spectrometer was inserted into the magnetron sputtering reactor to analyze the nature and energy distribution of each ion species impinging onto the substrate surface. It was find that at very low pressure (<5 mTorr), the ion energy spectra of the sputtered species showed a wide, bimodal distribution with a low energy component corresponding to the sheath potential and a much higher energy component arising from particles ejected from the target and only slightly thermalized in the gas phase. At higher pressure, all energy distributions became narrower due to a nearly complete thermalization. The Bi⁺-to-Fe⁺ ratio was also found to decrease with increasing pressure, going from about 4 at 3 to 1 at 30 mTorr. A similar feature was observed for the O⁺-to-O₂ ⁺ ratio. The plasma dynamic results have been correlated to the Rutherford backscattering spectroscopy characterization of BFO thin films.