Mechanisms for electron energy transport and electron energy distributions in magnetically enhanced inductively coupled plasmas

Abstract

Summary form only given, as follows. Magnetically Enhanced Inductively Coupled Plasma (MEICP) and helicon sources typically have higher plasma densities for a given power deposition than conventional inductively coupled plasma (ICP) sources. In industrial sources magnetic fields typically span a large range of values and modes are likely not pure. Power deposition has contributions from both non-collisional heating and electrostatic TG mode damping. Mechanisms for power deposition and electron energy transport in MEICPs have been computationally investigated using a 2-dimensional plasma equipment model. 3-d components of the inductively coupled electric field are produced from an m=0 antenna and 2-d applied magnetic fields. A Monte Carlo simulation is used to generate electron energy distributions (EEDs), transport coefficients and electron impact source functions. The electrostatic component of the wave equation is resolved by estimating the charge density using a harmonic perturbed electron density. In simulations performed for Ar plasmas, collisional damping may be the dominant heating mechanism at moderate pressures (>2 mTorr). However, at lower pressures Landau damping is an increasingly more important heating mechanism. In this regime, electrons have sufficiently long mean free paths that, if their thermal speeds are near the wave phase velocity, Landau damping may occur over a broad range of energies (10-100 eV). Therefore, heating occurs for large subset of the EED in addition to creating beamlike distributions. Evidence of noncollisional heating by the axial electric field is seen in the raising of the tails of the EEDs in the downstream region. Results indicate that the effect of the TG mode is to restructure power deposition near the coils. However, the propagation of the helicon component is little affected, particularly at large magnetic fields where the TG mode is damped. The raising of the tail of the EED is still observed.