Improving the impact energy by using auxiliary electrode in a cylindrical bore

Summary form only given. Plasma immersion ion implantation (PIII) is a promising technique for surface modification of materials. Because of its non line-of-sight process, there is the intriguing possibility of implanting "interior" surfaces. If the radius R of a bore is many Debye lengths, the bore will be plasma-filled and it is possible to implant into the sidewalls of the bore. Sheridan (1993) has found that the important length scale is the ion-matrix overlap, D=(/spl epsiv//sub 0//spl phi//en/sub 0/)/sup 1/2/ where /spl phi/ is the (negative) target potential and n/sub 0/ is the (uniform) plasma density. His recent research results indicate that ion implantation in small bores (R/spl les/D) is not very hopeful because the ion-matrix sheath overlap reduces the impact energy of the ions. We are proposing to use an auxiliary electrode, a conductive cylindrical bore which potential is always zero at the axis of the cylindrical bore, to improve the impact energy. We have calculated the structure of the ion-matrix sheath in an infinitely long cylindrical bore (R/spl les/D) with the auxiliary electrode and analyzed the dependence of its radius on the electric field in the bore. Our results show that the auxiliary electrode improves the distribution of the potential and electric field in the cylindrical bore.