Pulsed metal ion source by triggerless shunting arc discharge

The shunting arc is an arc discharge that is self-ignited in a low pressure gas without any trigger source. Possible application of the shunting arc to a pulsed ion source for plasma based ion implantation will be discussed. A 35 mm long titanium (Ti) wire 0.05 mm in diameter is heated by means of pulsed current from a 20 μF capacitor (1.5–3.0 kV) in an argon environment with pressure from 2.7 to 1300 Pa. Arc ignition was indicated by an abrupt decrease of the wire voltage accompanied by an abrupt increase of the arc current. Ultraviolet light spectroscopy has shown that a plasma containing Ti ions and neutrals is produced by means of the arc discharge. The maximum arc current is about 2.1 kA with arc voltage of 200–300 V. The wire temperature is estimated at about 1500 K, well below the melting point of Ti. The wire therefore remains in a solid phase during the arc discharge so that the wire can be used repeatedly. Ions are extracted from the plasma by a 5 kV, 10 μs negative high voltage pulse applied to a target. Shunting arc ignition using materials other than Ti will also be discussed.