Ponderomotive Effects in Electromagnetic Accelerator

Summary form only given. ICP plasma source of new type for dry etching has been developed. It operates at frequency 2 MHz and is driven by planar inductive coil, which is placed at the top of the channel formed by two coaxial dielectric cylinders. This coil creates RF magnetic field having mainly radial component in the channel and induces azimuthal RF current in plasma. At sufficiently low pressure (about 1 mtorr) this causes substantial ponderomotive force acting on azimuthally moving electrons and directed toward the bottom of the channel. Due to charge separation, the ambipolar electric field is sustained, which retards electrons and accelerates ions. The source represents electrodeless electromagnetic accelerator (EMA) and can be used for creating axially directed fluxes of ions. EMA has been modeled as axisymmetric ICP discharge in Ar gas using finite element method (FEM) of solving Maxwell equations for first harmonic of magnetic field and basing on experimental data of plasma density and electron temperature profiles. Magnetic field and RF current densities obtained have been used for simulation of Lorentz force acting on electrons and calculation of resulting ambipolar plasma potential. Simulations of electron trajectories in this combined electric and magnetic field show that electrons are trapped in the EMA channel and make a number of oscillations before leaving the channel. Trapping of electrons in ICP plasma has been recently reported by other researchers for slab geometry. Thus formed ponderomotive potential produces acceleration of ions in the channel up to 10-20 eV depending on RF power deposited in the plasma