Dual frequency ICP discharges: Effect of pressure and gas ratio on EEPF and discharge parameters

Using a radio frequency (rf) compensated Langmuir probe, the effects of operating parameters such as gas pressure and gas ratio on electron energy probability functions (EEPFs) and discharge parameters are investigated in Ar/CF4 discharges produced by a dual frequency/dual antenna large area (450 mm) inductively coupled plasma (ICP) source. It is observed that increasing pressure reduces the energy spread of EEPFs, due to increasing electron energy loss via collisions, from 20 eV at 1 mTorr to 13 eV at 25 mTorr. At a constant rf power, plasma density (ne) increases linearly with pressure between 1 and 10 mTorr and then (> 10 mTorr) decreases. The same trend has also been observed for electron temperature. It has also been found that increasing Ar gas proportion in the Ar/CF4 mixture significantly increases the plasma density (ne), however, the influence on plasma temperature and plasma potential was marginal.