Improvement of power transfer efficiency using a parallel resonance in a 60 MHz capacitively coupled plasma

A parallel resonance circuit is applied to improve the power transfer efficiency of 60 MHz capacitively coupled plasma. As the plasma resistance is inversely proportional to electron density, power transfer efficiency decreases with increasing input power. A parallel variable vacuum capacitor (VVC) is connected to the inductive load to improve power transfer efficiency. The inductive load is a series circuit consisted of a power line (usually denoted as an inductor), electrode, and plasma. As the capacitance of VVC approaches the parallel resonant point, the resistance of the parallel resonant circuit becomes much higher than without VVC, and the current flowing through the matching network decreases. Therefore, power transfer efficiency and electron density were increased. In addition, this effect is increased with increasing input power. At 100W, the power transfer efficiency and the electron density increase by 4.5% and 3.9%. However, at 200W, the power transfer efficiency and the electron density increase by 7.5% and 21%.