SIMS micro-analysis with a gallium ion microprobe

Abstract

SIMS microanalysis is readily achieved by the adoption of the liquid metal field ion source for formation of the primary ion probe. These sources exhibit high brightness and small source size and permit the formation of high intensity sub-micron ion beams at low energies (⩽10 KeV). Operation is simple, UHV compatible and well suited to mulit-technique surface analysis systems, as well as dedicated SIMS instrumentation. Beam characteristics for a gallium probe allow image resolutions down to 1000 Å with probe currents ranging from 50 pA at high resolution, to maximum currents in excess of 100 nA. Image recording times range from 10 s to 10 min, typically. A gallium source has been in routine operation for over one year on a quadrupole based SIMS instrument, and a wide range of experience gained on various specimens. These include metals, semiconductors, insulators, polymers and biological materials. Some comparisons have been made between the use of argona and gallium beams with respect to spectral content and elemental sensitivities. In general the sensitivities are similar, while the main difference in spectral content is the presence of secondary ions of gallium and gallium complexes. Insulating specimens which have proved very difficult in Auger analysis such as optical fibres, or powders, have been studied more readily with the gallium probe in SIMS analysis. In this case charge neutralization is effected with an accurately positioned 500 eV electron beam.