Generation of surface modes and plasma uniformity in VHF CCP reactors studied with a EM PIC code

CCP reactors represent one of the main instruments in the plasma processing industry, where they are utilized for a large number of different technologies involving etching or deposition processes. To increase the process rates, one can resort to increasing the ion fluxes to electrodes by using very high frequency harmonics in the driving voltage. The nonlinear dynamics of the plasma sheaths can generate even higher harmonics in the current, leading to the excitation of surface modes existing due to the interaction between the plasma sheath and plasma bulk dynamics. If sufficiently strong, the surface modes can significantly affect the plasma ionization radial profile and thus potentially influence radial uniformity of fluxes and IEDFs of ions impinging on electrodes. In this work we investigate the mentioned characteristics in CCPs operated at a low pressure and driven by VHF harmonics by performing kinetic simulations with an implicit electromagnetic energy-conserving PIC/MCC code. In particular, we discuss generation of energetic electrons as a result of the nonlinear sheath dynamics coupled with the surface mode excitation and the related radial nonuniformities.