Effects of antenna coil turns on plasma density and antenna voltage in solenoidal inductively coupled plasmas

Abstract

The number of antenna coil turns, N, that affects the plasma density is a significant factor to design an inductively coupled plasma source. The equivalent resistance and inductance of a transformer circuit seen at the antenna coil are known to increase with N. This can enhance the power transfer efficiency. However, there is an undesired capacitive coupling between the antenna coil and the plasma. The antenna voltage related to the capacitive coupling is known to be proportional to N. In this work, to investigate the effects of N, the plasma density and the antenna coil voltage are measured by a floating probe and high-voltage probes, respectively. A terminal capacitor is used to suppress the capacitive coupling. As a result, the effects of N are clearly observed on the plasma densities and the voltages of the antenna coil. The plasma density was found to dramatically increase with N while the capacitive coupling is suppressed. The antenna voltage was not increased with N, and it was investigated by the ratio of the antenna voltage to the total voltage.