Repairing of etching-induced damage of high-k Ba0.5Sr0.5TiO3 thin films by oxygen surface plasma treatment

Ba_0.5Sr_0.5TiO₃ (BST) thin films were patterned for fabricating BST capacitors in a helicon-wave plasma system. The etching parameters were optimized to minimize the leakage current density and maximize etch rate. The optimization condition was Ar(80%)/Cl₂(20%) gas mixture, with a helicon-wave plasma power and a substrate bias rf power of 1500 W and 90 W, respectively. From results of the X-ray photoelectron spectroscopy, the physical ion bombardment is more effective than chemical reaction for removing Sr, while Ti can be removed by formation of volatile TiCl. Ba was mainly removed by chemically assisted physical etching (such as BaCl_x). Some etching residues consisting of Ba and Sr were found after the BST films were etched and increased leakage current density. Oxygen surface plasma treatment can effectively repair surface damage caused by etching, and reduce the leakage current density of the BST capacitor from 4.0 × 10^-7 to 3.0 × 10^-8 A/cm² at 1 MV/cm and increase the breakdown field to ∼2 MV/cm at 1.0 × 10^-6 A/cm².