Discharge characteristics of electronegative Mg–CF4 direct current magnetron sputtering by probe measurements

The discharge characteristics of Mg–CF4 direct current (DC) reactive magnetron sputtering, which is assumed to be a typical electronegative discharge, are investigated as a function of CF4/(Ar + CF4) discharge gas ratios using probe measurements. For comparison, the discharge characteristics of Mg–CF4 radio frequency (RF) magnetron sputtering are also investigated. The results of the probe measurements show that the plasma potentials (Vplasma) of Mg–CF4 DC discharges decrease with increasing CF4/(Ar + CF4) ratios and become negative relative to the ground potential for discharges with CF4/(Ar + CF4) ratios of ≥60% for all discharge pressures investigated (0.40, 1.20, and 2.00 Pa). In contrast, the Vplasma of Mg–CF4 RF discharges remains 30–40 V higher than the ground potential independent of the CF4/(Ar + CF4) ratio. The electron temperature obtained from the logarithmic plot of the probe current–voltage (I–V) characteristics ranges between 1.7 and 6.4 eV, whereas the negative-ion temperature ranges between 2.1 and 5.1 eV. Moreover, a high negative-ion/electron ratio of up to 130 was obtained from the ratio of the saturated negative-ion probe-current to the saturated electron probe-current for high CF4/(Ar + CF4) ratios. Investigations on the changes in Vplasma and cathode potential (Vcathode) reveal that the potential configurations of Mg–CF4 electronegative DC discharges are affected by the compositions of the discharge current fluxes. The conclusions emphasize the characteristics of the electronegative Mg–CF4 DC discharges. The results obtained in this study are valuable for widening the potential applications of electronegative DC magnetron sputtering.