Numerical investigation of ion-energy-distribution functions in single and dual frequency capacitively coupled plasma reactors

Ion-energy-distribution functions (IEDFs) are numerically investigated in capacitively coupled (cc) radio frequency (rf) Ar/CF4/N-2 discharges by a one-dimensional particle-in-cell/Monte Carlo model. The simulation considers electron-neutral collisions, various kinds of collisions of ions (Ar+, CF3+, N-2(+), F-, and CF3-) with neutral, positive-negative ion, and electron-ion recombination. The influence of pressure, applied voltage amplitude, and applied frequency on the Ar+, CF3+, and N-2(+) IEDFs is presented. The dependence on the frequency regime is investigated by simulations of the Ar/CF4/N-2 mixture in single (13.56 MHz) and dual frequency (2+27 MHz or 1+27 MHz) cc reactors. A comparison of the simulation results with analytical calculations in a collisionless rf sheath is discussed. The results show that the IEDFs shift toward the low energies with increasing pressure or decreasing applied voltage amplitude. The Ar+ and N-2(+) IEDFs exhibit secondary maxima due to the charge transfer collisions. The CF3+ IEDF has a peak at high energies in consistency with the average sheath potential drop. The IEDFs in the dual frequency regime are broad and bimodal.