Plasma immersion ion cleaning of oxidized steel surfaces using hexafluoroethane and argon plasmas

For many years it has been known that cleaning of substrates using plasma techniques prior to physical vapor deposition processes can significantly improve coating adhesion. This article investigates the use of hexafluoroethane and argon plasmas in a pulsed glow discharge cleaning process. Applied voltages varied from −2 to −8 kV with a constant chamber pressure of 10 mTorr and etching times ranged from 15 to 120 min. Results indicate that in most cases, the hexafluoroethane plasmas removed 25% more oxygen atoms than the argon plasmas at similar applied voltages. Most of the oxygen removal was observed within the first 15 min with diminishing removal with increased cleaning time beyond 30 min. Plasma analysis revealed that the principal plasma specie was CF3 and reaction products for oxygen removal were carbon dioxide and carbon monoxide. The hexafluoroethane plasmas were determined to clean through a chemically enhanced sputtering while argon plasmas cleaned by physical sputtering only.