Energy distribution of O- ions during reactive magnetron sputtering

Low, medium, and high energy O- ion populations were experimentally detected during magnetron sputtering of Al in an Ar/O-2 atmosphere. Based on calculations, the authors propose that nonsputtered O- ions originating from the target surface are accelerated in the cathode fall, while sputtered O- ions may be excluded as a significant contribution to the high energy ion population. Furthermore, the formation of medium energy O- ions is consistent with the notion of sputtered, in the cathode fall accelerated, and subsequently dissociated AlO- and AlO2- clusters. These findings may be of importance for understanding plasma energetics and growth involving electronegative species.