The symmetry of capacitively coupled radio frequency (CCRF) discharges can be controlled electric... more The symmetry of capacitively coupled radio frequency (CCRF) discharges can be controlled electrically by applying a fundamental frequency and its second harmonic with fixed but adjustable phase shift theta between the driving voltages to one electrode. In such a discharge a variable dc self-bias eta is generated as an almost linear function of theta for 0° <= theta <= 90° via the Electrical Asymmetry Effect. The control parameter for eta and the discharge symmetry is theta. Here electron dynamics in electrically asymmetric geometrically symmetric dual frequency discharges operated in argon at 13.56 and 27.12 MHz is investigated experimentally by a particle-in-cell simulation and by an analytical model. The electron dynamics is probed by the electron impact excitation rate of energetic electrons from the ground state into highly excited levels. At high pressures (collisional sheaths) the excitation dynamics is found to work differently compared with conventional CCRF discharges...
Journal of Physics D-applied Physics - J PHYS-D-APPL PHYS, 2010
In a capacitively coupled radio frequency (CCRF) discharge the number of positive and negative ch... more In a capacitively coupled radio frequency (CCRF) discharge the number of positive and negative charges lost to each electrode must balance within one RF period to ensure a constant total uncompensated charge in the discharge, Qtot, on time average. This balance is the result of a compensation of electron and ion fluxes at each electrode within one RF period. Although Qtot is constant on temporal average, it is time dependent on time scales shorter than one RF period, since it results from a balance of the typically constant ion flux and the strongly time dependent electron flux at each electrode. Nevertheless, Qtot is assumed to be constant in various models. Here the dynamics of Qtot is investigated in a geometrically symmetric CCRF discharge operated in argon at 13.56 and 27.12 MHz with variable phase shift theta between the driving voltages by a PIC simulation and an analytical model. Via the electrical asymmetry effect (EAE) a variable dc self-bias is generated as a function of ...
Using a combined experimental, numerical and analytical approach, we investigate the control of p... more Using a combined experimental, numerical and analytical approach, we investigate the control of plasma properties via the electrical asymmetry effect (EAE) in a capacitively coupled oxygen discharge. In particular, we present the first experimental investigation of the EAE in electronegative discharges. A dual-frequency voltage source of 13.56 MHz and 27.12 MHz is applied to the powered electrode and the discharge symmetry is controlled by adjusting the phase angle theta between the two harmonics. It is found that the bulk position and density profiles of positive ions, negative ions, and electrons have a clear dependence on theta, while the peak densities and the electronegativity stay rather constant, largely due to the fact that the time-averaged power absorption by electrons is almost independent of theta. This indicates that the ion flux towards the powered electrode remains almost constant. Meanwhile, the dc self-bias and, consequently, the sheath widths and potential profile can be effectively tuned by varying theta. This enables a flexible control of the ion bombarding energy at the electrode. Therefore, our work proves the effectiveness of the EAE to realize separate control of ion flux and ion energy in electronegative discharges. At low pressure, the strength of resonance oscillations, which are found in the current of asymmetric discharges, can be controlled with theta.
The symmetry of capacitively coupled radio frequency (CCRF) discharges can be controlled electric... more The symmetry of capacitively coupled radio frequency (CCRF) discharges can be controlled electrically by applying a fundamental frequency and its second harmonic with fixed but adjustable phase shift theta between the driving voltages to one electrode. In such a discharge a variable dc self-bias eta is generated as an almost linear function of theta for 0° <= theta <= 90° via the Electrical Asymmetry Effect. The control parameter for eta and the discharge symmetry is theta. Here electron dynamics in electrically asymmetric geometrically symmetric dual frequency discharges operated in argon at 13.56 and 27.12 MHz is investigated experimentally by a particle-in-cell simulation and by an analytical model. The electron dynamics is probed by the electron impact excitation rate of energetic electrons from the ground state into highly excited levels. At high pressures (collisional sheaths) the excitation dynamics is found to work differently compared with conventional CCRF discharges...
Journal of Physics D-applied Physics - J PHYS-D-APPL PHYS, 2010
In a capacitively coupled radio frequency (CCRF) discharge the number of positive and negative ch... more In a capacitively coupled radio frequency (CCRF) discharge the number of positive and negative charges lost to each electrode must balance within one RF period to ensure a constant total uncompensated charge in the discharge, Qtot, on time average. This balance is the result of a compensation of electron and ion fluxes at each electrode within one RF period. Although Qtot is constant on temporal average, it is time dependent on time scales shorter than one RF period, since it results from a balance of the typically constant ion flux and the strongly time dependent electron flux at each electrode. Nevertheless, Qtot is assumed to be constant in various models. Here the dynamics of Qtot is investigated in a geometrically symmetric CCRF discharge operated in argon at 13.56 and 27.12 MHz with variable phase shift theta between the driving voltages by a PIC simulation and an analytical model. Via the electrical asymmetry effect (EAE) a variable dc self-bias is generated as a function of ...
Using a combined experimental, numerical and analytical approach, we investigate the control of p... more Using a combined experimental, numerical and analytical approach, we investigate the control of plasma properties via the electrical asymmetry effect (EAE) in a capacitively coupled oxygen discharge. In particular, we present the first experimental investigation of the EAE in electronegative discharges. A dual-frequency voltage source of 13.56 MHz and 27.12 MHz is applied to the powered electrode and the discharge symmetry is controlled by adjusting the phase angle theta between the two harmonics. It is found that the bulk position and density profiles of positive ions, negative ions, and electrons have a clear dependence on theta, while the peak densities and the electronegativity stay rather constant, largely due to the fact that the time-averaged power absorption by electrons is almost independent of theta. This indicates that the ion flux towards the powered electrode remains almost constant. Meanwhile, the dc self-bias and, consequently, the sheath widths and potential profile can be effectively tuned by varying theta. This enables a flexible control of the ion bombarding energy at the electrode. Therefore, our work proves the effectiveness of the EAE to realize separate control of ion flux and ion energy in electronegative discharges. At low pressure, the strength of resonance oscillations, which are found in the current of asymmetric discharges, can be controlled with theta.
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