Electron drift and the loss balance of charged particles in planar-unbalanced dc magnetron discharge

Abstract

The electron drift phenomenon is investigated in the downstream region of an unbalanced dc magnetron argon discharge. The spatially resolved measurements of the electron velocity distribution function (EVDF) using a planar probe reveal the existence of a strong on-axis electron drift parallel to magnetic field in spite of a very small axial variation less than 1 V in the plasma potential. The average drift velocities calculated from the asymmetry of the measured EVDFs show that there exists a significant electron drift from cathode to substrate with a maximum speed of about 1x10(6) m/s, which is comparable to the bulk electron temperature. The magnetic mirror force which is driven by the axial gradient of the magnetic field (i.e., the parallel delB force) is suggested as a possible source for the parallel electron drift. Carrying out a scaling of current densities with the measured data, it is found that the parallel delB force can produce the electron current enough to balance the discharge current, implying that the electron transport in the downstream region is determined not by the classical diffusion model in which electron motion toward the anode is diffusion and mobility dominated but by the modified diffusion model in which electron motion is drift dominated. (C) 2005 American Institute of Physics.