This dissertation proposes Current Source Type Pulse Generator circuit to improve the load voltage waveform by solving the voltage ringing problem of capacitively-coupled plasma system. Voltage source type pulse power supplies used in the plasma industry have short circuit current, voltage ringing problems with capacitively-coupled plasma load. The proposed circuit can solve these problems by circuit structure. In addition, to improve the load voltage and current waveform, the new PWM technique and circuit improvements are introduced in this research.
The capacitively-coupled plasma consists of two electrode, and they are spaced apart from each other. Plasma power supply generates a bulk plasma by applying a potential to both electrodes. It is structurally the same as a capacitor, and its electrical characteristics are also predominant in capacitor. Therefore, in order to operate a capacitively-coupled plasma system, a suitable power supply for capacitive load is required.
Current source converter uses the inductor component at DC-link. Therefore, the current variation of the DC-link is very small, so inductor can operate like stable current source. Because of this characteristics, current source converter can operate in stable state with capacitive load or voltage source. As mentioned above, the current source converter based power supplies can be applied to capacitively-coupled plasma load with some advantages.
Current Source Type Pulse Generator proposed in this dissertation consists of four detailed circuits. Those circuits are Bias Current Generator, Bias Current Modulator, Slope Current Generator, and Slope Current Modulator, respectively. They form the two constant current at DC-link, and output the two pulse currents to the load. Those output current contribute to generate the plasma load voltage that required by the capacitively-coupled plasma process.
The proposed circuit is verified by PLECS simulator and laboratory scale hardware system. To check the output waveform improvement, the Voltage Source Type Pulse Generator and Current Source Type Pulse Generator are operated under same conditions. The results are represented by load voltage and current waveforms. In addition, the entire system of Current Source Type Pulse Generator is designed and verified by simulation and experiments. Finally, the output waveforms meet the process requirements, and the results demonstrate that the proposed Current Source Type Pulse Generator circuit can be suitably used for capacitively-coupled plasma load that was initially aimed.