Negative hydrogen ion beam extraction from an AC heated cathode driven Bernas-type ion source

A plasma grid structure was installed to a Bernas-type ion source used for ion implantation equipment. A negative hydrogen (H−) ion beam was extracted by an AC driven ion source by adjusting the bias to the plasma grid. The extracted electron current was reduced by positively biasing the plasma grid, while an optimum plasma grid bias voltage for negative ion beam extraction was found to be positive 3 V with respect to the arc chamber. Source operations with AC cathode heating show extraction characteristics almost identical to that with DC cathode heating, except a minute increase in H− current at higher frequency of cathode heating current.