Enhancement of implantation energy using a conducting grid in plasma immersion ion implantation of dielectric/polymeric materials

Plasma immersion ion implantation (PIII) is conducted on insulating materials using a conducting grid to enhance the ion implantation energy. The biased grid that is connected to the sample holder enshrouds the insulating specimens, and ions from the overlying plasma are implanted through the grid into the samples. The implantation voltage is applied to the grid via the sample platen so problems associated with PIII of insulating materials such as capacitance and charging (and secondary electrons) effects can be greatly alleviated. In the work reported here, we investigate the efficacy of the grid approach. Secondary ion mass spectrometry is used to determine the nitrogen depth profiles. Simulation indicates that for insulating specimens that are plasma implanted without the conducting grid, the maximum nitrogen ion energy is only about 23 keV for an applied voltage of 40 kV while it improves to 30 keV in the presence of the grid. The experimental results are consistent with the surface potentials derived from theoretical modeling of the charging effects. To further improve the ion implantation energy, more effective grid dimension scaling and surface shielding, more optimal separation between the conducting grid and insulator surface, as well as better confinement of the secondary electrons are required.