Gallium ion extraction from a plasma sputter-type ion source

A broad mixed ion beam containing positive ions of gallium (Ga) was produced with a plasma sputter-type ion source. Liquid Ga was suspended on a tungsten reservoir to be sputtered and postionized in argon (Ar) plasma excited by a radio frequency (rf) power at 13.56 MHz. Optical emission spectra from the plasma near the Ga sputtering target had indicated that the release of Ga into plasma increased with increasing negative bias to the sputtering target. The ratio of Ga(+) current to Ar(+) current was measured to be about 1% with a quadrupole mass analyzer at 100 V extraction voltage for incident rf power as low as 30 W. Ions in the plasma were extracted through a pair of multiaperture electrodes. The homogeneity of Ga flux was examined by making a Ga deposition pattern on a glass substrate located behind the extractor electrodes.