Stabilization of charge on electrically insulating surfaces during SIMS experiments—experimental and theoretical studies of the specimen isolation method

Abstract

AbstractRecent experiments have shown that secondary ion mass spectrometric (SIMS) measurements of insulator surfaces can be greatly facilitated by the use of a charged aperture located immediately above the analysis area (the ‘specimen isolation technique’). This allows the surface potential within the aperture area to be stabilized. Charging is stabilized when the potential difference between the surface and the aperture becomes large enough that excessive charge, in the form of secondary electrons, is drained away from the surface to the aperture. The potential difference generated on such insulating surfaces can be measured experimentally by varying the voltages applied to the electrostatic analyzer to measure the secondary ion intensity as a function of kinetic energy. Such measurements have been carried out on a Cameca IMS‐3F instrument for a range of aperture dimensions and for different primary and secondary ions. The surface potential can be stabilized at a potential readily measurable by the electrostatic analyzer for both O− and Cs+ ion beams. The mechanism for this stabilization has been analyzed through calculations of two dimensional contours for the region around the specimen holder. For surfaces with a very high charging potential (>600 V), potential wells which can trap ions of low kinetic energy develop near the surface. Element and oxide secondary ion kinetic energy distribution curves, taken under specimen isolation conditions, which differ from those obtained under normal non‐charging SIMS conditions, are evidence for such ion trapping.