Production of ion beam using plasma filament ion source

A plasma filament ion source has been developed as a long-lived ion source for use in ion implantation. This ion source uses a primary discharge to serve as an electron source for a second discharge, which is formed into a plasma filament replacing a thermionic metallic filament used in the Freeman-type ion source. The operation is relatively facile and a good beam stability can be obtained. With any combination of a plasma filament of either argon or neon and a feed gas of either fluoride (AsF5, PF5, PF3 or BF3) or hydride (AsH3), the lifetime was found to be more than 90 hours with an extraction voltage of 40 kV and the corresponding ion current density over 20 mA/cm2. This ion source could produce appreciable amounts of As+, B+, P+ and O+ ions, yielding analyzed currents of 10.0, 3.0, 2.6 and 3.0 mA, respectively. This device proved to be eminently suitable for oxygen ion production and also useful for ion implantation incorporated with full cryopumping. Furthermore, the role of the electron temperature of the plasma filament was shown to be of importance in the dissociation and ionization of the feed gas molecules. (author)