Asymmetric Bipolar Plasma Power Supply to Increase the Secondary Electrons Emission in Capacitive Coupling Plasmas

Power supplies have played crucial role to improve and extend plasma applications. Several dc, pulsed, and radio frequency (RF) stabilized power supplies have been developed over a wide range of frequencies and voltage waveforms. However, the influence of voltage waveform on the plasma densification, mainly due to the secondary electrons emission from the electrodes, has not been quite explored. This paper proposes an asymmetric pulsed bipolar power supply, adjustable in frequency, amplitude, pulsewidth, and number of pulses for generation of cold plasmas. Short period positive pulses, between longer negative pulses, increase greatly the secondary electron emission from the electrodes and, consequently, the plasma ionization rate. Short pulses (ns) are obtained by the phase shift between each carrier, and the high-intensity pulses are obtained by cascading the cell submodules in a half-bridge cascade topology, using a modular half-bridge converter configuration. The intensity of the positive and negative pulses can be varied independently. There is no unintended dc voltage level between the electrodes, which appear in RF plasmas. The plasma generated in this way is free of electric arc and can be kept stable within a broader range of operating parameters, mainly the voltage and the working gas pressure.