Non-linear effects in ICP: theory and experiments

Summary form only given. Operation of a low pressure inductively coupled plasma (ICP) at low driving frequency leads to increased values of the RF magnetic field and thus to enhancement of nonlinear effects due to RF Lorentz force typically negligible at 13.56 MHz. In recent years ICP experiments in low frequency regime have demonstrated generation of strong upper harmonics of the electrostatic potential and electric current in the ICP skin layer. A significant modification of the plasma profile by ponderomotive force has been demonstrated in a low frequency ICP, but the ponderomotive force found in experiment appeared to be significantly smaller than that predicted by classical formula for cold plasma. We review recently obtained experimental results on nonlinear effects in a low frequency cylindrical ICP with a planar coil and present a theory of these phenomena. We show that generation of nonlinear harmonics in RF potential and RF current are due to action of different parts of the RF Lorentz force; its potential part gives rise to potential oscillations, while its solenoidal part (existing only in a dissipative plasma) is responsible for generation of nonlinear current. A generalized theoretical model for nonlinear effects in two-dimensional cylindrical ICP, accounting for potential and solenoidal parts of the RF Lorentz force, has been formulated within a magneto-hydrodynamic approach.