Abstract:
We demonstrate that if charging caused by electron irradiation of an insulator is controlled by a
defocused flux of soft-landing positive ions, secondary electron (SE) images can contain contrast
due to lateral variations in (i) changes in the SE yield caused by subsurface trapped charge and (ii)
the SE-ion recombination rate. Both contrast mechanisms can provide information on microscopic
variations in dielectric properties. We present a model of SE contrast formation that accounts for
localized charging and the effects of gas ions on the SE emission process, emitted electrons above
the sample surface, and subsurface trapped charge. The model explains the ion flux dependence of
charge-induced SE contrast, an increase in the sensitivity to surface contrast observed in SE images
of charged dielectrics, and yields procedures for identification of contrast produced by localized
sample charging.
