Local electron and ion density control using passive resonant coils in inductively coupled plasma

Abstract

Control of local electron and ion density using passive resonant coils is experimentally investigated in an inductive argon discharge. Four passive resonant coils are installed under a powered coil; each coil has a fan shape and good azimuthal symmetry. Electron energy probability functions and two-dimensional ion density profiles were measured under both resonant and non-resonant regimes. At non-resonance, almost all of the current flows through the powered coil located in the center of the reactor, and the profiles of the electron and ion density are convex. However, at resonance, a large current flows through the passive resonant coil, and dramatic changes are observed in the electron and ion density profiles. At resonance, the electron and ion densities near the passive resonant coil are increased by 300% compared to the non-resonant condition, and radial distributions become almost flat. Experimental results show that the electron and ion density profiles can be effectively controlled by a passive resonant coil at both low pressure (5 mTorr) and high pressure (50 mTorr). These changes in electron and ion density profiles can be understood by the changes of the electron heating and ionization regions.