Rf multipolar plasma for broad and reactive ion beams

Hot cathode dc multipolar plasma sources are very efficient but have lifetime and contamination problems when they are operated with chemically active gases. As an alternative solution the rf excitation of a triode structure immersed in a multicusp magnetic field has been developed. The structure has an internal cathode, an anode around which are the magnet lines, and a third electrode which is either the target electrode in the case of 'plasma processing' or the beam forming electrode in the case of 'ion beam processing'. The source has been operated with oxygen and fluorocarbon gases without any lifetime problems. The discharge may be run down to 10-4 torr (within source chamber) and creates a plasma which is homogeneous to +- 1.5% over 175 mm diameter section and which delivers at the beam forming electrode a current density of about 1 mAcm-2 for 500 W rf power. (author)