Caption title. [Patent no.] 5,449,411 ; [date of patent]: Sep. 12, 1995. At head of title: United States patent [19], Fukuda et al. Photocopy.

A microwave plasma processing apparatus is provided with a vacuum chamber, a substrate holder for mounting a substrate to be processed, a reactive gas feed port, a cleaning gas feed port, a plasma generation device for generating a processing plasma from the reactive gas and a cleaning plasma from the cleaning gas, and a high-frequency electric field application device for applying an electric field having a frequency that allows ions in the cleaning plasma to follow changes in the electric field. The high-frequency electric field application device is activated to apply the electric field to the cleaning plasma so as to remove substances that have been deposited on the surfaces of the vacuum chamber and substrate holder due to the processing of the substrate by the processing plasma, thereby cleaning up the vacuum chamber and substrate holder.