Particle-in-cell numerical simulation of non-uniform plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is attracting more attention as a surface processing technique. During PIII, the plasma is not frequently uniform due to hardware limitations, although numerical simulation of PIII processes is usually based on a uniform plasma environment. This may lead to incorrect and incomplete understanding of the PIII process and dynamics. In this work, numerical simulation is conducted using the particle-in-cell (PIC) model to consider the effects of non-uniform plasma in the vacuum chamber. The plasma source that is installed on top of the chamber produces down-stream plasmas with density diminishing from top to bottom. The simulation results demonstrate that the non-uniform plasma gives rise to an evidently different plasma sheath configuration and consequently different implantation dynamics compared to the uniform plasma case. The incident dose on the top surface is not uniform and the dose peak appears at a certain distance away from the target edge initially and gradually moves towards the central zone as time elapses. In comparison with uniform plasma implantation, the dose non-uniformity is more severe in the non-uniform plasma case although the plasma is uniform horizontally. This is due to the different focusing effects of the plasma sheath that depends on the plasma distribution.