Co-axial ECR plasma system for radioactive ion implantation

A pulsed, co-axial electron cyclotron resonance (ECR, 2.45 GHz) plasma reactor was designed and tested to demonstrate the feasibility of plasma-based radioactive ion implantation (P-32 radioisotope). The geometry of the reactor was designed to produce an efficient implantation of cylindrical implants. Therefore, the reactor is cylindrical in shape, and is equipped with a cylindrical grid in a co-axial geometry. The plasma is created between the wall and the grid; the plasma surrounds the implant, allowing for a radial implantation. A 1 ms microwave pulse creates a plasma in argon, which sputters material from a radioactive cathode. A fraction of the radioisotopes is then ionized, and the ions are implanted into negatively biased metal samples. The plasma was characterized by means of electrostatic probes, giving spatial evaluations of the electron temperature, plasma potential and electron density. Titanium samples were implanted with P-32 during a study that aimed at optimizing the position of the radioactive sputter cathode in the plasma. From an analysis of the distribution of the radioactive fragments, we deduce that the plasma potential has a marked effect on the ion trajectories. In particular, it provides a more uniform implantation distribution than one would otherwise expect. For plasma densities similar to 8 x 10(10) cm(-3), implantation efficiencies as high as 1% are measured; this is about 100 times higher than conventional beam-line ion implantation.