Etching characteristics and plasma-induced damage of Ba 0.65Sr 0.35TiO 3 thin films etched in CF 4/Ar/O 2 plasma

Abstract

Sol–gel-derived Ba 0.65Sr 0.35TiO 3 (BST) thin films were etched in CF 4/Ar/O 2 plasma using magnetically enhanced reactive ion etching technology. The maximum etch rate of BST film is 8.47 nm/min when CF 4/Ar/O 2 gas mixing ratio is equal to 9/36/5. X-ray photoelectron spectroscopy analysis indicates the accumulation of fluorine-containing by-products on the etched surface due to their poor volatility, resulting in (Ba,Sr)-rich and (Ti,O)-deficient etched surface. Compared to the unetched counterparts, the etched Ba 3d 5/2, Ba 3d 3/2, Sr 3d 5/2, Sr 3d 3/2, Ti 2p 3/2, Ti 2p 1/2 and O 1s photoelectron peaks shift towards higher binding energy regions by amounts of 1.31, 1.30, 0.60, 0.79, 0.09, 0.46 and 0.50 eV, respectively. X-ray diffraction (XRD) analysis reveals that intensities of the etched BST (1 0 0), (1 1 0), (2 0 0) and (2 1 1) peaks are lowered and broadened. Raman spectra confirm that the Raman peaks of the etched film shift towards lower wave number regions with the values of 7, 6, 4 and 4 cm −1, and the corresponding phonon lifetimes are longer than those of the unetched film because of the plasma-induced damage. When the etched films are postannealed at 650 °C for 20 min under an O 2 ambience, the chemical shifts of Ba 3d, Sr 3d, Ti 2p and O 1s peaks, the variations for atomic concentrations of Ba, Sr, Ti and O, and the Raman redshifts are reduced, while the corresponding XRD peak intensities increase. It is conceivable that the plasma-induced damage of the etched film could be partially recovered during the postannealing process.