Planar RF induction plasma coupling efficiency

The radiofrequency power coupling efficiency of a planar induction source is determined by measurement of the power dissipated in the matching network and inductive coupler. Typically one finds the radiofrequency current to vary between 20 and 60A (root mean Square). The equivalent resistance of the coupling network is determined to be 0.09 Omega, and power coupling efficiency to the plasma is therefore found to be 70-90% with the remaining power lost to ohmic heating of the circuit elements. The efficiency is highest when the plasma-to-inductor distance is least since the increased mutual inductance reduces the radiofrequency inductor current and, hence, ohmic losses. Efficiency of power coupling is nearly constant as a function of radiofrequency power between 200 and 2000 W. Somewhat larger currents are required to sustain a discharge at lower pressures (about 1 m Torr) or when the plasma is not magnetically confined, giving rise to lower coupling efficiencies.