Numerical study of dual-frequency capacitively-coupled discharges in electronegative SF 6

Discharge structures and properties of dual-frequency capacitively-coupled plasma (CCP) discharges in SF 6 are studied by using a one-dimensional Particle-in-Cell/Monte Carlo (PIC/MC) method. The simulations are carried out at a gas pressure of 25 mTorr for a fixed low-frequency (LF) source of 3.2 MHz and a high-frequency (HF) source of 27–50 MHz. Results show that in dual-frequency discharges both sources nonlinearly interact even if the source frequencies are significantly different from each other ( e.g. , 3.2 and 50 MHz). In the presence of the LF source, the electron density in the bulk plasma reduces in comparison with the density for the case without LF source. The non-equilibrium behavior between the electron-SF 6 collisional ionization or attachment and density diffusion is found for a HF source frequency higher than 49 MHz. The electron temperature in the bulk plasma is higher than 5 eV, which sustains the discharge by compensating the loss of electrons due to strong attachment.