Development of a microwave ion source for negative oxygen ion beam production

A volume production type microwave negative ion source has been developed for negative ion beam processes such as ion implantation and ion beam deposition, etc. In order to increase efficiency of negative oxygen ion production, we employed a double plasma cell system in which two plasma cells were connected to each other. A high density primary plasma was generated in the first plasma cell with 2.45 GHz microwave power and negative ions were effectively generated in the second plasma cell. A filter magnetic field of about 0.1 T was applied on the second plasma cell to prevent diffusion of high energy electrons from the first plasma cell. Oxygen negative ion beams were generated by this method and the maximum oxygen (O−) ion current of 142 μA (current density: 325 μA/cm2) was extracted continuously from the ion source at an extraction voltage of 30 kV and a microwave power of 500 W. This value was three orders larger than that obtained by a single plasma cell system without the filter magnetic field. Molecular oxygen ions (O−2 and O−3) were also obtained at percentages of about 20% and 2% of the major O− ion intensity.