Performance characteristics of a plasma-type sputter ion source

Abstract

A low-power, plasma-type sputter source for the production of positive ions of non-volatile elements has been constructed and tested. Argon and copper were employed as support gas and sample material, respectively. The source output was measured as a function of the discharge current, the axial magnetic field, the sputter voltage, the spacing between the sputter sample and the source exit, the diameter of the sputter sample, and the argon pressure. It was found that the Cu + current, I Cu, increases with increasing discharge current i d as I Cu ∝ i d n , where n ⩾ 2. I Cu increases with decreasing sample-to-exit spacing s. For not too small spacings, I Cu ∝ s −2. Cu + currents of up to 6 μA were produced at a total power consumption of less than 60 W. The simultaneous prese nce of an intense Ar + component in the beam causes space charge expansion which becomes significant at low energies and large ratios of the drift length to the beam-size defining apertures. Loss of target current may also be caused by neutralization of ions in charge-transfer collisions outside of the source.