Lorentz force effect on electron energy distribution in low pressure inductively coupled plasmas

Summary form only given, as follows. Depletion of the electron energy probability function (EEPF) by slow electrons in the skin layer has been observed in low pressure inductively coupled plasmas at low driving frequency. The experiments are carried out in a cylindrical ICP with a planar coil maintained at frequency 0.45 MHz, a fixed discharge power P = 200 W, and argon pressure p = 1 mTorr corresponding to a nearly free flight regime for ions and electrons. The EEPFs measured with a Langmuir probe at a fixed radial position of maximal RF electric field and different axial positions are shown. No depletion of the EEPF is observed along the axis where azimuthal electric field vanishes. The observed peculiar depletion of EEPF by low energy electrons in the skin layer occurs only at low gas pressures and low driving frequencies. The results of calculations based on analytical solution to the collisionless Boltzmann equation in the skin layer using integrals of the electron motion are also shown. The effect is explained by anisotropy and time-dependency of the electron distribution function, induced by strong RF magnetic fields and oscillating electrostatic potential of doubled frequency in the skin layer. The found phenomenon gives another proof of the importance of nonlinear and hot plasma effects in weakly collisional ICP.