Increase of Boron Ion Beam Current Extracted from a Multi‐Cusp Ion Source in an Ion Doping System with Mass Separation

A multi‐cusp ion source with large area extraction area has a capacity to extract high current ion beams. However it is difficult to obtain high current boron ion beams from boron trifluoride plasma as input power density is low and $BF2+$ is a main ion species. It was found that fluoride ion currents were selectively decreased by applying positive potential to a plasma electrode with respect to a plasma chamber. Using this method to a multi‐cusp ion source with adequate magnet configuration, high current boron ion beams of 500 μA/cm were obtained.