Ion energy distributions in inductively coupled plasmas having a biased boundary electrode

In many plasma materials processing applications requiring energetic ion bombardment such as plasma etching, control of the time-averaged ion energy distributions (IEDs) to surfaces is becoming increasingly important to discriminate between surface processes having different threshold energies. Inductively coupled plasmas (ICPs) are attractive in this regard since the plasma potential is low and so the energy of ion fluxes can be more finely tuned with externally applied biases. In these situations, pulsed plasmas provide another level of control as the IEDs from different times during the pulse power period can be combined to create the desired time-averaged IED. A recent development in controlling of IEDs in ICPs is the use of a boundary electrode (BE) in which a continuous or pulsed dc bias is applied to shift the plasma potential and modify the IEDs to surfaces without significant changes in the bulk plasma properties. Combinations of pulsing the ICP power and the BE bias provide additional flexibility to craft IEDs. In this paper we discuss results from a computational investigation of IEDs to a grounded substrate in low-pressure (a few to 50mTorr) ICPs sustained in argon. Results are compared with experimental measurements of plasma properties and IEDs. We demonstrate the ability to customize IEDs consisting of three energy peaks corresponding to the plasma potential during the plasma active glow, plasma afterglow and the plasma potential with the applied boundary voltage.