Ion trajectories in plasma ion implantation of slender cylindrical bores using a small inner end source

Plasma immersion ion implantation (PIII) into slender cylindrical bores with higher efficiency is described in this letter. The use of an inner end plasma source excited by a radio-frequency hollow cathode is investigated theoretically and experimentally. The end source that is covered by a small grounded shielding electrode to ensure steady discharge enables continuous delivery of the required plasmas, and the potential difference in the tube increases the ion impact energy. Particle-in-cell simulation demonstrates that the ion trajectories are complex due to the special electric field configuration that is composed of three regions characterized by ion acceleration, no electric field, and ion deceleration. The end source structure with the open shielding electrode is insufficient to achieve high ion energy, although it is effective in maintaining a steady discharge in the source. Hence, a shielding electrode with a protruding electrode structure is required to conduct high energy PIII; a cylindrical bore with an inner diameter of 20 mm is successfully implanted.