3-D Numerical Simulation on Plasma Immersion Ion Implantation Batch Treating Process of Bearing Balls

In the plasma immersion ion implantation (PIII) process, since the dose distribution is affected by the sheath around the sample to be treated, controlling the sheath expanding process is very important for obtaining a good dose uniformity. In this paper, a 3-D particle-in-cell (PIC) model was established to study the sheath expanding process around balls of the bearing in a PIII batch treating process respectively. Using the finite difference method, the spatial distributions of the normalized potential and ion density in the simulation region were calculated by solving Poisson's Equation, Newton's motion equations and the Boltzmann assumption for the electrons. The influences of the magnitude and pulse width of the implantation voltage applied as well as the plasma density on the sheath conformability were studied. The simulation results show that the sheath conformability around the balls in batch treating process is worse than that in a single process due to the sheath overlap of neighbor bearing components. The bad conformability of the sheath would lead to a bad distribution of the incident dose on the surface of bearing balls. In order to guarantee the conformability of the sheath around the bearing balls, a small pulse width, enough display distance as well as proper implantation voltage and plasma density should be promised in the PIII batch treating process.