Current-voltage relations in magnetrons

The current-voltage relationship in a magnetron plasma appears to be strongly dependent on the dynamics of the sputtered particle-gas atom interaction. Large fluxes of energetic (several eV) sputtered atoms from the cathode heat the gas in the near cathode region, resulting in a significant reduction in the local gas density as a function of discharge current (and hence particle flux). This reduction in gas density results in a lower rate of ion formation, and hence a more resistive plasma. Thus, the rate of voltage increase with current in a magnetron is related to the magnitude of the gas density rarefaction, which is dependent on the cathode sputter yield, sputtered atom energy, the cross section for sputtered atom-gas collisions, the molecular velocity of the gas, and the gas density. A model has been developed which describes the observed rate of voltage increase in a magnetron as a function of this thermalization process. © 1988, American Vacuum Society. All rights reserved.