Discharge characteristics of bucket‐type ion source using a microwave plasma cathode

A large diameter and long‐life ion source is considered desirable for plasma processes. The advent of better filamentless ion sources is desired due to frequent utilization of reactive gases. We have proposed a bucket‐type ion source which uses a microwave plasma cathode in place of a conventional filament. This paper experimentally examined the V–I characteristics of arc discharge. An arc current of 2‐5 A was obtained at an arc voltage of 60‐150 V. The V–I characteristics were comparable to that of a conventional bucket‐type ion source using a filament. The V–I characteristics and the electron density distribution in the arc plasma are changed depending on the shape of the electron extraction electrode which was coaxially placed in the arc discharge chamber (200 mm diameter). The electrode diameter was optimized at 40 mm for this chamber. Two kinds of ion beams, argon and oxygen, were extracted from the ion source and both their beam current densities were over 1 mA/cm². These values are sufficient for practical applications to ion beam milling.