Monte-Carlo Simulation of positive ion transport through SF6 plasma sheath: application to the deep silicon etching

Amand Pateau1,2, Ahmed Rhallabi1, Marie Claude Fernandez1, Mohamed Boufnichel2,Fabrice Roqueta2
Page no. 78-89

Ion transport across the sheath is studied using sheath Monte-Carlo model coupled to the plasma kinetic model. The advantage of the developed simulation approach is the prediction of IEDF and IADF onto the substrate surface as a function of the operating conditions (RF power, gas pressure and flow rate). The model is applied to SF₆ ICP plasma which is widely used in material etching processes like the silicon etching. IEDF evolution at each incident angle versus SF₆ pressure is analysed. The bimodal peak due to the modulation of the DC voltage through the sheath is evidenced. The two peaks around the average energy qV_C become almost symmetric when the pressure increases. This is due to the diminution of the electron density with the pressure because of the electronegativity of SF₆ leading to the increase of the sheath thickness. The results also show the correlation between the ion mass and the width of IEDF bimodal peak. The latter is all the more wide that the ion is light. Furthermore, the simulation results show that incident energy E_i at the sheath edge strongly affects the anisotropy degree of IEDF. The latter is more anisotropic for a low E_i.                                                                                                                                                            

                                                                                                     Keywords: Plasma, SF₆, Sheath, Etching, Simulation, Modelling