Method of and apparatus for controlling plasma potential and eliminating unipolar arcs in plasma chambers

Abstract

A method of and apparatus for controlling the potential of a plasma including a metal-walled chamber and a conductive coil which carries a radio-frequency current and is wrapped around the metal-walled chamber to produce a plasma within the chamber. A filament made of refractory metal has two ends, and a central portion formed in the shape of a probe. The central portion of the filament extends into the interior of the chamber and the two ends of the filament pass through a wall of the chamber to the exterior of the chamber. A heating power supply is connected to the two ends to the filament and to the chamber wall for heating the filament to a predetermined temperature above that of the plasma. The heated filament produces thermionic emissions from the filament to the plasma in order to control the plasma potential and eliminate unipolar arcing at the chamber wall.

I claim: 
     
       1. Apparatus for controlling the potential of a plasma including a metal-walled chamber having an interior and an exterior, and a conductive coil adapted to carry a radio-frequency current wrapped around the metal-walled chamber to produce a plasma within said chamber; comprising: a filament made of refractory metal and having a first end, a second end, and a central portion formed in the shape of a probe, said central portion of the filament extending into the interior of the chamber and said first and second ends of the filament passing through a wall of the chamber to the exterior of the chamber; and   a heating power supply connected to said first and second ends of the filament and to the chamber wall for heating said filament to a predetermined temperature above that of the plasma, producing thermionic emissions from the filament to the plasma.