Numerical Simulation of an RF Capacitive Discharge in CO₂ Using the Hydrodynamic Code SIGLO-rf

We investigated the processes occurring in an RF capacitive discharge in carbon dioxide using the SIGLO-rf hydrodynamic code, which is the 1D user-friendly simulation software of capacitively coupled RF discharges developed by JP Boeuf and LC Pitchford at the University of Toulouse and based on the same physics as in [Phys. Rev. E 51 1376 (1995)]. The dependences of the coefficients of ionization and attachment of electrons on the reduced electric field, as well as the coefficients of ion-ion, ion-electron recombination and detachment of electrons in carbon dioxide, were added for calculations in the gas parameters file. The calculated RF discharge extinction curve is in good agreement with our measured curve, which confirms the suitability of both the code and the gas parameters introduced into it for describing processes in plasma. It is shown that at low CO2 pressures (below 0.1 Torr), stochastic heating of electrons in expanding near-electrode sheaths dominates. At higher gas pressures, stochastic heating is pronounced only at high RF voltages (several hundred volts), and the main heating of electrons occurs in double layers, which are formed both in the anode phase of the sheath and in the plasma volume. The maximum number of double layers appearing in the discharge gap during one RF half-cycle reached 3.