Plasma immersion ion implantation into cylindrical bore using internal inductively-coupled radio-frequency discharge

Plasma immersion ion implantation (PIII) is a potentially excellent interior surface treatment technique due to no line-of-sight restriction. However, some problems have been encountered due to the low ion energy and ion fluence non-uniformity especially for treatment of the interior wall of a thin tube. In this paper, a new method for inner surface PIII using internal inductively-coupled radio-frequency (RF) discharge is described. A cylindrical inductive coil inserted inside the tube serves as both the plasma source and grounded electrode to avoid overlapping of the plasma sheath fronts propagating from opposite sides. The effects of the gas species, gas pressure, RF power, and number of coil turns are investigated. Our results demonstrate the feasibility of this novel inner surface treatment method and the number of turns in the coil has a critical influence on the discharge behavior. If the number of turns is little, the plasma density is low and non-uniform inside the tube due to the relatively intense capacitively-coupled RF discharge at the two ends. In contrast, the plasma density and uniformity are evidently improved by using more turns in the coil.