Plasma implantation of cylindrical bore - a reality?

Summary form only given. Plasma immersion ion implantation has successfully been applied to treat the outer surface of objects with an irregular geometry. Theoretical and experimental investigations have also demonstrated the capability to implant the inner surfaces of cylindrical bores. However, practical implementation of the process is not straightforward due to the finite plasma volume confined within the bore and the large non-uniformity of plasma density in the bore. The incident ions hardly obtain the full acceleration voltage since the plasma sheath expands rapidly, and to make things worse, it is difficult to apply a high voltage on the inner wall if the bore radius is too small or the plasma density is too low, as confirmed by our numerical analysis. Besides, the plasma in the bore depletes abruptly once the negative pulse is applied. This time scale is smaller than 1 /spl mu/s that is approximately the rise time of the implantation pulse. This further lowers the energy of the incident ions and requires more powerful power modulators, for instance, one capable of producing a rise time of less than 1 /spl mu/s; otherwise, the implantation process may end before the pulse voltage reaches the voltage plateau. The design of such a piece of hardware is difficult in practice.