Effects of reactive gas addition on ionization of metal atoms in droplet-free metal ion sources

This paper reports on influences of reactive oxygen (O2) or nitrogen (N2) addition on ionization characteristics of sputtered titanium (Ti) atoms in an argon (Ar)-based novel droplet-free metal ion sources. Although Ti atoms had a pressure dependence of ionization characteristics similar to copper ones in a pure Ar discharge, the ionization characteristics of Ti atoms were affected by adding reactive N2 and O2 gases into the Ar plasma. Especially, the reactive gas addition significantly reduced fluxes of Ti atoms and Ti+ ions probably due to target-poisoning effect caused by chemical reactivity of Ti. Even adding the reactive gases, the source will still work as a droplet-free metal ion source since the ionization fraction of Ti atoms reached over ∼ 90%. Optimization of discharge conditions and reactive gas provision will be necessary from a metal ion process point of view.