Noncollisional heating and electron energy distributions in magnetically enhanced inductively coupled and helicon plasma sources

Abstract

The ability to deposit power in the volume of plasma reactors at locations deeper than the conventional skin depth makes magnetically enhanced inductively coupled plasma (MEICP) and helicon sources appealing for use in materials processing. Mechanisms for power deposition and electron energy transport in MEICPs have been computationally investigated using a two-dimensional (2D) plasma equipment model. Using a tensor conductivity in the solution of Maxwell’s equations, three-dimensional components of the inductively coupled electric field are produced from an m=0 antenna and 2D applied magnetic fields. These fields are then used in a Monte Carlo simulation to generate electron energy distributions (EEDs), transport coefficients, and electron impact source functions. The electrostatic component of the wave is resolved by estimating the charge density using an oscillatory perturbed electron density. For MEICPs operating at pressures less than 10 mTorr in Ar, significant power deposition occurs downstream when the radial and axial components of the electric field are commensurate with the azimuthal component. For magnetic fields above 100 G, the tail of the EED (>20–30 eV) is enhanced in the downstream region. This enhancement results from noncollisional heating by the axial electric field for electrons in the tail of the EED which have long mean free paths, while lower energy electrons are still somewhat collisional.