Modelling and optimization of inductively coupled loop antenna plasma sources

Inductively coupled plasma sources are attractive for plasma processing of materials because they can be optimized to generate high-density plasmas at low neutral species pressure that are spatially uniform, with high efficiency, low ion bombarding energy and relatively low expense. Based on the data shown in the companion paper, we describe computer modelling using the cylindrical fully kinetic code ANTENA that demonstrates the advantages of the spiral loop design over several other inductive source geometries that include single and double concentric loop designs. The models also make extrapolation to other and larger designs fairly straightforward. We claim that electrostatic effects due to plasma scrape-off onto plasma limiters near the antenna blades induce a large and dominant radial electric field E_r. This E_r is a finite-electron-temperature effect and is not present in the purely inductive cold plasma picture. The highly uniform radial density profiles that we measure are shown to be consistent with edge-peaked ionization profiles. It may be possible to exploit this fact to optimize more uniform plasma processing sources.