Oxygen ion source with plasma cathode

An ion source with a plasma cathode has been developed for long lifetime use in ion implanters. In this ion source, a plasma cathode replaces the conventional metallic filament used in a Freeman-type ion source. This ion source consists of two compartments, namely a plasma generator and an ion source chambers interconnected by a tapered narrow duct. The pressure difference between the two parts, maintained by differential pumping, prevents the feed gas from flowing into the plasma generator. With any combination of an argon plasma cathode and a feed gas of either fluoride (AsF 5, PF 5) or oxygen, the lifetime was found to be more than 90 h with an extraction voltage of 40 kV and a correspoding ion current density of 20 mA/cm 2, and a considerable amount of As +, P +, O +, and O 2 + ions were observed in mass spectra.