Coupling Characteristics of Induction Coil in Atmospheric Pressure Inductively Coupled Plasmas

Summary form only given. The coupling characteristics between induction coil and radio frequency (RF) discharges generated by inductively coupled plasma technique (ICP) at the initial start-up phase in near atmospheric pressure range is investigated experimentally. A rapid increase of the plasma loading resistance and decrease of the effective coil loading inductance were observed during the dynamic change of plasma from electrostatic (E) to electromagnetic (H) mode. During this dynamic mode transition, frequency and phase shift from their resonance value, thereby deviating the output RLC circuit including RF induction coil from its ideal resonance condition. The total load of the inverter power source becomes slightly capacitive, thereby increasing the switching losses of the static inverter transistor (SIT) inverter elements. As a result, the power coupling efficiency between plasma and RF source (P_abs/P_RF) as well as the power efficiency of the RF source (P_RF/P_DC) strongly deteriorates, thereby decreasing the effective plasma production efficiency. Having employed a constant-current high-power immittance conversion circuit shows successful improvement of the power efficiency in induction plasma generation. A frequency sweeping experiment bringing the driving frequency close to resonance one also improve the coupling efficiency of the induction coil as well as the power efficiency of inverter power source, which enhances the plasma heating and production efficiency