Direct current plasma implantation using a grounded conducting grid

A novel plasma implantation technique performed in a low pressure steady state dc mode utilizing a grounded conducting grid on top of the wafer stage is presented. By numerically simulating the ion paths by the particle-in-cell method, it is observed that the ion paths are optimized for certain implant geometry. In the optimal configuration, the directional angle of the acceleration vector does not depend on the mass and charge state of the ions, and the ratio of the partial differential of the scalar potential φ along the radial and longitudinal directions remains constant for varying applied voltages. The retained dose and impact energy uniformity are totally determined by the ratio of the radius of the wafer stage r, radius of the vacuum chamber R, distance between the wafer stage and the grid H, and thickness of the wafer stage D. The optimal ratio is r:R:H:D=1:4:2.5:2, that is, suggesting a disk shape vacuum chamber, which is quite different from that of a conventional plasma immersion ion implanter. In addition to retaining the large area and parallel processing advantages of plasma immersion ion implantation (PIII), the implantation energy can be extended far beyond the limit of PIII as the technique obviates the use of the power modulator, which not only limits the implantation energy but also is the most expensive and technologically complex hardware component in a PIII system.