Numerical study of Ar/CF4/N2 discharges in single- and dual-frequency capacitively coupled plasma reactors

A one-dimensional particle-in-cell/Monte Carlo model is developed to study capacitively coupled (cc) radio-frequency discharges in a gas mixture of Ar, CF4, and N-2. The charged species, which are followed in the model, are: Electrons and Ar+, CF3+, N-2(+) F-, and CF3- ions. The simulation considers electron - neutral (Ar, CF4, and, N-2) collisions, various kinds of collisions of ions with neutrals, positive-negative ion recombination, and electron-ion recombination. The model yields results for electron and ion densities, fluxes and energy distributions, collision rates and electric field, and potential distributions. The simulations are performed for a 0.8/0. 1/0.1 ratio of Ar/CF4/N-2 mixture at a pressure of 30 mTorr in single (13.56 MHz) and dual frequency (2+27 MHz) cc reactors and a comparison between the two frequency regimes is made. Results show that the structure of the discharges is electronegative in both cases. F-1 and CF3- ions are the main negative charge carriers in the single and dual frequency regime, respectively. In the presence of low-frequency (2 MHz) and a strong electric field, the light F- ions are no longer confined in the bulk plasma and they partially respond to the instantaneous electric field. The calculated electron energy probability function profiles can be approximated to a Druyvesteyn and bi-Maxwellian distribution with high-energy tails in the single- and dual-frequency regime, respectively. The ion energy distribution is narrow with one outstanding peak in the single-frequency scheme, whereas it is wide and bimodal in the dual-frequency scheme. (C) 2003 American Institute of Physics.