Reactive ion etching was used to etch barium strontium titanate thin films in a CHF3/Ar plasma.BST surfaces before and after etching were analyzed by X-ray photoelectron spectroscopy to investigate the reaction ion etching mechanism,and chemical reactions had occurred between the F plasma and the Ba,Sr and Ti metal species.Fluorides of these metals were formed and remained on the surface during the etching process.Ti was almost completely removed because the TiF4 by-product is volatile.Minor quantities of Ti?F could still be detected by narrow scan X-ray photoelectron spectra,and Ti?F was thought to be present in the form of a metal-oxy-fluoride.These species were investigated from O1s spectra,and a fluoride-rich surface was formed during etching.BaF2 and SrF2 residues were difficult to remove because of their high boiling point.The etching rate was limited to 12.86 nm/min.C?F polymers were not found on the surface,indicating that the removal of BaF2 and SrF2 was important for further etching.A 1-min Ar/15 plasma physical sputtering was carried out for every 4 min of surface etching,which effectively removed remaining surface residue.Sequential chemical reaction and sputtered etching is an effective etching method for barium strontium titanate films. Reactive ion etching was used to etch barium strontium titanate thin films in a CHF3 / Ar plasma.BST surfaces before and after etching were analyzed by X-ray photoelectron spectroscopy to investigate the reaction ion etching mechanism, and chemical reactions had occurred between the F plasma and the Ba, Sr and Ti metal species. Fluorides of these metals were formed and remained on the surface during the etching process. Ti was almost completely removed because the TiF4 by-product is volatile. Resin quantities of Ti? F could still be detected by narrow scan X-ray photoelectron spectra, and Ti? F was thought to be present in the form of a metal-oxy-fluoride. These species were investigated from O1 spectra, and a fluoride-rich surface was formed during etching.BaF2 and SrF2 residues were difficult to remove because of their high boiling point. The etching rate was limited to 12.86 nm / min. C polymers were not found on the surface, indicating that the removal of BaF2 and SrF2 was important for further etching. A 1-min Ar / 15 plasma physical sputtering was carried out for 4 min of surface etching, which for strong removal of residual surface residue. Sequential chemical reaction and sputtered etching is an effective etching method for barium strontium titanate films.