Influence of magnetic field strength on capacitively coupled CF4 discharge at different pressures

The influence of a homogeneous magnetic field parallel to the electrodes on the plasma properties and electron heating mode was investigated by a one-dimensional particle-in-cell/Monte Carlo simulations in electronegative CF4 discharges. The discharge conditions are Z = 3.5 cm, f = 13.56 MHz, V0=300  V, and the various gas pressure of 10 mTorr, 100 mTorr and 200 mTorr. It is found that, in the absence of a magnetic field, the discharges are electronegative at different pressures and the electronegativity is stronger at higher pressure. When a homogeneous magnetic field is applied, the electron density significantly increases and the electronegativity decreases to varying degrees at different pressures. At p = 10 mTorr and p = 100 mTorr, a transition from a hybrid combination of α and drift-ambipolar (DA) modes into a pure α mode is induced by a weak magnetic field. At p = 200 mTorr, a transition from a DA mode into a hybrid combination of α and DA modes is induced by a relatively high magnetic field. The strength of the magnetic field required to induce mode transition becomes stronger at higher gas pressures. This is because increasing the pressure reduces the mean free path and the frequent electron-neutral collisions disrupt electron gyromotion, thus the effects of the magnetic field are greatly reduced.