Planar RF induction plasma coupling efficiency

Abstract

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 60 A (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 mTorr) or when the plasma is not magnetically confined, giving rise to lower coupling efficiencies.