PREDICTIONS OF ION ENERGY-DISTRIBUTIONS AND RADICAL FLUXES IN RADIO-FREQUENCY BIASED INDUCTIVELY-COUPLED PLASMA-ETCHING REACTORS

Inductively coupled plasma (ICP) reactors are being developed for low gas pressure (<10s mTorr) and high plasma density ([e] > 10(11) cm(-3) ) microelectronics fabrication. In these reactors, the plasma is gener ated by the inductively coupled electric field while an additional rad io frequency (rf) bias is applied to the substrate. One of the goals o f these systems is to independently control the magnitude of the ion f lux by the inductively coupled power deposition, and the acceleration of ions into the substrate by the rf bias. In high plasma density reac tors the width of the sheath above the wafer may be sufficiently thin that ions are able to traverse it in approximately 1 rf cycle, even at 13.56 MHz. As a consequence, the ion energy distribution (IED) may ha ve a shape typically associated with lower frequency operation in conv entional reactive ion etching tools. In this paper, we present results from a computer model for the IED incident on the wafer in ICP etchin g reactors. We find that in the parameter space of interest, the shape of the IED depends both on the amplitude of the rf bias and on the IC P power. The former quantity determines the average energy of the IED. The latter quantity controls the width of the sheath, the transit lim e of ions across the sheath and hence the width of the IED. In general , high ICP powers (thinner sheaths) produce wider IEDs. (C) 1996 Ameri can Institute of Physics.