Estimating electron drift velocities in magnetron discharges

Electron motion in magnetron discharges is complicated. In a first approximation, single particle motion can be considered in given electric and magnetic fields to estimate drifts. Based on magnetic and electric field measurements for discharges in an unbalanced magnetron with a strong magnet it is shown that, for the most energetic electrons, the del B and curvature drift velocities can be comparable to or even larger than the commonly mentioned E x B drift velocity. In the fluid approximation, the electron pressure gradient adds yet another drift component. Since all of those drifts are generally additive, the term E x B drift can be generically used but should be understood to include other drifts. Strong velocity gradients and direction reversal can be found, which suggest velocity shear as a source of waves and instabilities, likely creating the density-fluctuation seeds for ionization zones seen in high power impulse magnetron sputtering. (C) 2012 Elsevier Ltd. All rights reserved.