Magnetic control of nonlinear electron resonance heating in a capacitively coupled radio frequency discharge

Abstract

In magnetized capacitively coupled radio frequency (RF) plasmas operated at low pressure, the magnetic asymmetry effect (MAE) provides the opportunity to control the discharge symmetry, the DC self-bias, and the ion energy distribution functions at boundary surfaces by adjusting a magnetic field, that is oriented parallel to the electrodes, at one electrode, while leaving it constant at the opposite electrode. This effect is caused by the presence of different plasma densities in regions of different magnetic field strength. Here, based on a balanced magnetron magnetic field configuration at the powered electrode, we demonstrate that the magnetic control of the plasma symmetry allows to tailor the generation of high frequency oscillations in the discharge current induced by the self-excitation of the plasma series resonance (PSR) through adjusting the magnetic field adjacent to the powered electrode. Experimental current measurements performed in an argon discharge at 1 Pa as well as results of an equivalent circuit model show that nonlinear electron resonance heating can be switched on and off in this way. Moreover, the self-excitation of the PSR can be shifted in time (within the RF period) and in space (from one electrode to the other) by controlling the discharge symmetry via adjusting the magnetic field.

Electron power absorption dynamics in magnetized capacitively coupled radio frequency oxygen discharges

“…Moreover, the ion flux can be adjusted in this way [20]. Oberberg et al [21] also found that tuning such axially non-uniform magnetic fields in low pressure CCPs allows to control the self-excitation of the plasma series resonance (PSR) and Non-Linear Electron Resonance Heating (NERH) in space and time due to the magnetic control of the plasma symmetry [22,23]. Other recent studies reported that a homogeneous B-field can lead to an asymmetry in CCP discharges and can improve the control of the ion energy and flux at boundary surfaces [24].…”

Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code

“…The mirror force acting along the field lines does not have much influence on the electron motion in the longitudinal channels during the sheath expansion because the energy of their longitudinal motion acquired due to the electron acceleration by the sheath expansion is much larger than the transverse kinetic energy, so that their pitch angle is small. However, the magnetic field strongly affects the transverse electron dynamics above the racetrack, which significantly changes the resonant behavior of the corresponding current channel [40,83,84]. The lack of the PSR excitation in the transverse current channel observed here can be attributed to the shift of the corresponding resonance frequency caused by the magnetic field (see the companion paper [33]).…”

“…To produce it, one needs a simple external network with a blocking capacitor sustaining the self-bias, and an asymmetry in the sheath behavior. The reactor geometry was chosen to model the experimental facility described in [40,55,56], see Fig. 1.…”

“…Because of this fact and the complexity of the overall electron heating dynamics, we omit such processes from the present numerical model to be able to concentrate on new electron heating/energization mechanisms inherent to the rfMS discharges and to show that they can be well sustained without secondary electron emission. The magnetic field is chosen to model the field relevant to the experimental device described in [40,55,56] and is approximated using the vacuum solution series similar to [69]. The corresponding coefficients are given in Appendix A and it is assumed that due to the low kinetic pressure of plasma in the region where it is well magnetized, the magnetic field modifications due to the plasma currents were negligible.…”

“…Further, there is a strong electron heating observed at the moment when the powered sheath starts to expand along the magnetic field lines. This heating can be linked to the nonlinear electron resonance heating (NERH) and the related plasma series resonance (PSR) [37,38,39,40] mechanism and also increases mostly the longitudinal velocity, so that the majority of the accelerated electrons leave the discharge. Some of them are sufficiently deflected and trapped by the magnetic field, so that they can follow the arclike magnetic field and collide with the expanding sheath on the other side of the EMCR region, leading to an enhancement of the sheath energization efficiency.…”