Dislocation imaging with a scanning proton microprobe using channeling scanning transmission ion microscopy (CSTIM)

Abstract

Scanning transmission ion microscopy (STIM) combined with channeling has previously been demonstrated to be able to map regions of relatively poor crystal quality due to beam induced damage [1,2]. This paper describes the implementation of the CSTIM technique on the Oxford scanning proton microprobe and its ability to image misfit dislocations at the interface of an epitaxial Si 0.85Ge 0.15 layer grown on a (001) silicon substrate. Proton energy loss maps are generated by detecting transmitted protons with the beam aligned with a major axis or plane of the crystal. The bending of the crystal lattice planes due to the presence of dislocations causes dechanneling of the beam, giving protons transmitted through these regions a greater energy loss than those transmitted through regions of good crystallinity. Groups of dislocations give rise to bands of contrast along the [110] and [110] directions. Changes in contrast on tilting the specimen are consistent with the dislocations being of the 60° type rather than edge type, in agreement with the TEM results obtained from this specimen. By imaging misfit dislocation “cross” patterns in a Si 0.95Ge 0.05 layer grown on a silicon substrate, it has been shown that the minimum number of dislocations in a group that can be imaged is approximately 5 with a beam size of about 0.3 μm.