Effects of tube length and radius for inner surface plasma immersion ion implantation using an auxiliary electrode

Plasma immersion ion implantation of the inner surface of a finite-length small cylindrical tube with a coaxial, grounded auxiliary electrode is modeled using a two-dimensional particle-in-cell model. Various ratios of tube lengths against tube diameters are simulated. It is found that a peak in total accumulated dose is observed near the ends of the tube. Provided that it is long enough, the ions that come from the outside of the tube cannot pass through the middle-plane. That is, the tube can be divided conceptually into an "end" and a "middle" region, while the middle remains empty and all the flux goes to the end. In other words, a one-dimensional model can be applied to the "middle" region. The simulation results including the enhanced ion dose agrees with our experimental data.