AN UNBALANCED MAGNETRON SPUTTERING DEVICE FOR LOW AND MEDIUM PRESSURES

The discharge characteristics of an unbalanced magnetron sputtering de vice, equipped with a 100-mm-diam planar circular target and with two electromagnetic coils, have been analyzed in a range of operation pres sures from 0.02 to 1 Pa. The variation of discharge extinction and ign ition pressures and target voltage is presented as a function of the r atio of currents in the magnetron coils and discharge current. A maxim um discharge current beyond which it is not possible to sustain the di scharge at low pressures has been observed, This extinction current in creases with operating pressures. An explanation for the effect is bas ed on the loss of gas from the plasma due to gas heating with energeti c sputtered particles and subsequent gas density rarefaction in the ne ar target region. Higher pressure is thus necessary to keep constant g as density in the magnetron plasma when the discharge current is incre ased. The magnetic field configuration is presented for several values of the ratio of currents in the magnetron coils and correlated to the variation of discharge extinction and ignition pressures, extinction current, and target voltage. The low pressure operation of the magnetr on strongly depends on optimization of the magnetic field shape on the sputtered target. The deposition rate of titanium films is a linear f unction of magnetron power up to 2.5 kW and does not depend on Ar pres sure in the pressure range studied (0.08-0.6 Pa). (C) 1995 American In stitute of Physics.