An unbalanced magnetron sputtering device for low and medium pressures

Abstract

The discharge characteristics of an unbalanced magnetron sputtering device, equipped with a 100-mm-diam planar circular target and with two electromagnetic coils, have been analyzed in a range of operation pressures from 0.02 to 1 Pa. The variation of discharge extinction and ignition pressures and target voltage is presented as a function of the ratio of currents in the magnetron coils and discharge current. A maximum discharge current beyond which it is not possible to sustain the discharge at low pressures has been observed. This extinction current increases with operating pressures. An explanation for the effect is based on the loss of gas from the plasma due to gas heating with energetic sputtered particles and subsequent gas density rarefaction in the near target region. Higher pressure is thus necessary to keep constant gas density in the magnetron plasma when the discharge current is increased. 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 magnetron strongly depends on optimization of the magnetic field shape on the sputtered target. The deposition rate of titanium films is a linear function of magnetron power up to 2.5 kW and does not depend on Ar pressure in the pressure range studied (0.08–0.6 Pa).