Theoretical investigation of plasma immersion ion implantation of cylindrical bore using hollow cathode plasma discharge

Plasma immersion ion implantation of the internal surface of a cylindrical bore with a small diameter is difficult. The use of radio-frequency hollow cathode discharge as the internal plasma source for ion implantation is proposed. The implantation dynamics and plasma sheath expansion are investigated numerically using the particle-in-cell model. The inner diameter of the tube in our simulation is 20 mm and the external diameter of the hollow cathode is 12 mm. Three electric field zones are observed due to the existence of the electrode with ground potential in the tube. The ions undergo acceleration in the region close to the hollow cathode, maintain their velocity in the zone without the electric field due to overlapping of the plasma sheath, and decelerate in the region near the open end of the tube. Most of the ions are implanted into the surface away from the open plane of the hollow cathode. This is attributed to the special configuration of vertical electric field. The simulation results have demonstrated that plasma immersion ion implantation using a hollow cathode can be effectively applied to the treatment of the inner wall of a cylindrical bore, especially the ones with a small diameter.