Two Dimensional Computer Simulation of Plasma Immersion Ion Implantation

Department of Physics and Chemistry, Engineering Faculty of Guaratinguet´a FEG, UNESPAv. Ariberto Perreira da Cunha 333, Guaratinguet´a, SP, BrasilReceived on 30 January, 2004; revised version received on 6 May, 2004The biggest advantage of plasma immersion ion implantation (PIII) is the capability of treating objects withirregular geometry without complex manipulation of the target holder. The effectiveness of this approach relieson the uniformity of the incident ion dose. Unfortunately, perfect dose uniformity is usually difficult to achievewhen treating samples of complex shape. The problems arise from the non-uniform plasma density and ex-pansion of plasma sheath. A particle-in-cell computer simulation is used to study the time-dependent evolutionof the plasma sheath surrounding two-dimensional objects during process of plasma immersion ion implanta-tion. Before starting the implantation phase, steady-state nitrogen plasma is established inside the simulationvolume by using ionization of gas precursor with primary electrons. The plasma self-consistently evolves toa non-uniform density distribution, which is used as initial density distribution for the implantation phase. Asa result, we can obtain a more realistic description of the plasma sheath expansion and dynamics. Ion currentdensity on the target, average impact energy, and trajectories of the implanted ions were calculated for threegeometrical shapes. Large deviations from the uniform dose distribution have been observed for targets withirregular shapes. In addition, effect of secondary electron emission has been included in our simulation and noqualitative modifications to the sheath dynamics have been noticed. However, the energetic secondary electronschange drastically the plasma net balance and also pose significant X-ray hazard. Finally, an axial magneticfield has been added to the calculations and the possibility for magnetic insulation of secondary electrons hasbeen proven.