Tantalum etching with a nonthermal atmospheric-pressure plasma

Tantalum was etched in a downstream, atmospheric-pressure plasma. In this process, etching occurred without significant ion bombardment. An etching rate of 6.0±0.5 μm/min was achieved using 14.8 Torr oxygen, 22.4 Torr carbon tetrafluoride, 720±5 Torr helium, 685 W radio frequency power at 13.56 MHz, and a film temperature of 300 °C. The etching rate increased with the applied power, carbon tetrafluoride pressure, oxygen pressure, and residence time of the gas between the electrodes, indicating that the surface reaction depends on the density of reactive fluorine species generated in the plasma. X-ray photoemission spectroscopy revealed that the etched surface was covered with tantalum fluoride and to a lesser extent, tantalum oxide. Based on these observations, a mechanism for tantalum etching is proposed which involves the reaction between fluorine atoms and the adsorbed tantalum fluoride.