Characterization of Ga-Bi Liquid Metal Alloy Ion Source

Liquid metal alloy ion sources (LMAIS) are now of increasing interest in mass-separated focused ion beam (FIB) systems where a variety of projectile ions can be used. Typically, these can be focused into diameters of the order of 10 nm, with current densities of several A/cm2 giving probe currents of 1 pA -30 nA.
A Gallium-Bismuth LMAIS with melting point temperature of 222°C has been studied. The ion source was based on a mechanical treated Ta emitter. The emission characteristics of the source were investigated. From a detailed analysis of the source mass spectra as a function of emission current, the mechanism of single and double-charged ions emission is established. Good agreement is obtained comparing these results with Swanson’s investigations of a pure Bi source.
GaBi LMAIS allows to provide FIB structuring of a silicon substrate using either shallow donor ions (Bi) or acceptors ions (Ga) without changing the ion source.