Note that in the embodiment ofthe present invention, not only the O.sub.2 gas but also inert gas such as Ar and He or mixed gas of the O.sub.2 gas and the inert gas can also be used.(2-8) Plasmatization of the O.sub.2 GasThe high frequency power is applied to the cylindrical electrode 215 from the high frequency power supply 273 via the matching unit 272 (the electric field is formed in the proces