POWER TRANSFER EFFICIENCY AND MODE JUMP IN AN INDUCTIVE RF DISCHARGE

A large-diameter (50 cm) high-density (>10(11) cm(-3)) plasma is produ ced in a few mTorr argon by inductive RF discharge using a conventiona l external antenna or a plasma-immersed internal antenna. A power tran sfer efficiency, i.e., the ratio of net power deposited into plasma to total power into the matching circuits, is measured as a function of the electron density based on a test antenna method. The measured dens ity dependence of the power efficiency is well described by an equival ent circuit where both inductive and capacitive couplings are included with stochastic power deposition process taken into account. The inte rnal antenna, for the conditions studied, has higher power efficiency than the external antenna and enables a stable discharge at low pressu res without density jump. The density jump observed in the external an tenna discharge is attributed to the mode transition between a capacit ive discharge and an inductive discharge. A mechanism of the density j ump is successfully explained in terms of the density dependence of th e power transfer efficiency.