Development of bipolar accelerator for pulsed ion beam implantation

Intense pulsed ion beams (PIB) are expected to be applied. for pulsed ion beam implantation to semiconductor since an anneal-less implantation process is expected. In the application the purity of the ion beam is very important, however, the purity of conventional PIB is very poor. To improve the purity a new type of PIB accelerator named "bipolar pulse accelerator (BPA)" is proposed. The accelerator consists of two acceleration gaps (first gap and post acceleration gap) and a drift tube placed between the gaps. High power bipolar pulse is applied to the drift tube to accelerate ions. In the accelerator intended ions are selectively accelerated and the purity of the ion beam is enhanced. As the first step of the development of the accelerator, magnetically insulated acceleration gap is developed. The gap has an ion source of coaxial gas puff plasma gun on the grounded anode and a negative pulse is applied to the cathode to accelerate ions. By using the plasma gun, ion source plasma (nitrogen plasma) of current density around 100 A/cm² is produced, which is injected to the anode. After the plasma injection, negative pulse of voltage 220 kV, duration 60 ns is applied to the cathode. In the paper, preliminary results of the experiment are described including the waveforms of the system and shadowgraph measurement. From the results principle of the acceleration of ion beam in the BPA is confirmed.