Investigation of the sustaining mechanisms of dc magnetron discharges and consequences for I-V characteristics

The influence of the starting conditions and sheath thickness on the magnetron discharge is investigated using a Monte Carlo program. The average number of ionizations caused by an electron emitted from the cathode is calculated. It is shown that the sheath thickness plays a crucial role in the generation of ions and the sustainment of the discharge. An analytical formula is obtained which relates discharge voltage, sheath thickness and ion-induced secondary electron coefficient. From it, a natural explanation for the very steep current-voltage (I-V) characteristic in magnetron discharges follows. Comparison with experiment suggests an anomalous diffusion of electrons across the sheath. The simulations were done for a rotatable cylindrical magnetron, but the results should be valid for planar magnetrons as well