Electric field filamentation and higher harmonic generation in very high frequency capacitive discharges

The formation of electric field transients at very high frequencies are reported recently in literature. In present work we have studied the effects of the discharge voltage on the formation and nature of electric field transients in a symmetric, collision-less, very high frequency, capacitively coupled plasma using a self-consistent particle-in-cell (PIC) simulation code. At a driving frequency of 60 MHz and at 5 mTorr of gas pressure (argon), the applied discharge voltage is varied from 10 V to 150 V for a fixed discharge gap between electrodes. It is observed that an increase in the discharge voltage causes filamentation in the electric field transients and to create multiple higher harmonics in the bulk plasma. Correspondingly, higher harmonics, up to 7th harmonic, in the discharge current are also observed. The power in the higher harmonics increases with a rise in the discharge voltage. The plasma density continues to increase with the discharge voltage but in a non-linear manner, whereas, the bulk electron temperature decreases. Meanwhile, the electron energy distribution function (EEDF) evolves from a Maxwellian at lower discharge voltages to a bi-Maxwellian at higher discharge voltages. (author)