THE DETERMINATION OF THE CURRENT-VOLTAGE CHARACTERISTICS OF A CLOSED-FIELD UNBALANCED MAGNETRON SPUTTERING SYSTEM

An investigation has been carried out into the current-voltage (I-V) c haracteristics of a closed-field unbalanced magnetron sputtering syste m (CFUBMS). CFUBMS is a versatile technique for the high-rate depositi on of high quality metal, alloy and ceramic coatings. A key factor in this system is the ability to transport high ion currents to the subst rate. This can enhance the formation of fully dense coatings at relati vely low values of homologous temperature. A study has been made of th e parameters that determine the I-V characteristics of this system, at both the target and the substrate. From this, empirical relationships have been developed to describe the substrate ion current density and the substrate self-bias potential. Measurements have been taken of th e discharge voltage, the substrate self-bias voltage, and substrate cu rrent using aluminium, zirconium, tungsten, and copper targets, at tar get currents of up to 8 A, over the pressure range 0.5-3 mTorr, and at substrate-to-target separations of 80 mm, 110 mm and 150 mm. The disc harge voltage, V-T, follows the established relationship I-T = beta(V- T-V-0)(2), where I-T is the discharge current and V-0 is the minimum v oltage required to strike a discharge. The variations of beta and V-0 with target material and pressure are discussed. At the substrate, a l inear relationship, I-s = mI(T), was observed between the ion current drawn at the substrate, I-s, and the discharge current, I-T, where the coefficient of proportionality, m, varies with chamber pressure and s ubstrate-to-target separation. Also, self-bias voltages, in the range -17 to -30 V, were measured. The value was largely independent of targ et material and substrate-to-target separation, but depended strongly on chamber pressure. (C) 1998 Elsevier Science S.A.