Comparison of the operating characteristics of an opposed target magnetron using ferromagnetic and non-ferromagnetic targets

The operation of an opposed target magnetron with a specially designed uniform magnetic field perpendicular to rectangular targets has been studied in DC and pulsed DC operation for non-ferromagnetic (copper) and ferromagnetic (mild steel: 99.5% Fe) target materials. The sputtering gas was Ar with pressures in the range 0.26–0.4 Pa, the regulated current range up to 6 A, pulsed frequencies from 50 kHz to 250 kHz and pulse widths range 496–8016 ns. lse duty cycles above 0.9, the I–V characteristics for copper targets show a region of negative resistance, indicating a high ionization density in the plasma bulk even through the pulse-off time. As the duty cycle is reduced below 0.9, this negative resistance property is lost. The mild steel targets display I–V characteristics without a negative resistance region. ove behaviour is analysed and discussed for both the Fe and Cu targets, using Optical Emission Spectroscopy (OES), time-resolved OES in the centre of the plasma bulk and ion energy spectra at the substrate region. nclusions show that comparable sputtering rates can be obtained for copper and thick (12 mm) Fe targets. For Fe targets, the energy density of the ion current at the substrate is twice the one for copper. These effects are related to a less efficient magnetic confinement when using ferromagnetic targets due to imperfections in the choice for the magnetic poles design.