Angular Dependence of the Ion-Induced Secondary Electron Emission for He+ and Ga+ Beams

Angular Dependence of the Ion-Induced Secondary Electron Emission for He+ and Ga+ Beams

Castaldo, V.
Withagen, J.
Hagen, C.
Kruit, P.
Van Veldhoven, E.

Applied Sciences

IST/Imaging Science and Technology

2011-06-16

In recent years, novel ion sources have been designed and developed that have enabled focused ion beam machines to go beyond their use as nano-fabrication tools. Secondary electrons are usually taken to form images, for their yield is high and strongly dependent on the surface characteristics, in terms of chemical composition and topography. In particular, the secondary electron yield varies characteristically with the angle formed by the beam and the direction normal to the sample surface in the point of impact. Knowledge of this dependence, for different ion/atom pairs, is thus the first step toward a complete understanding of the contrast mechanism in scanning ion microscopy. In this article, experimentally obtained ion-induced secondary electron yields as a function of the incidence angle of the beam on flat surfaces of Al and Cr are reported, for usual conditions in Ga+ and He+ microscopes. The curves have been compared with models and simulations, showing a good agreement for most of the angle range; deviations from the expected behavior are addressed and explanations are suggested. It appears that the maximum value of the ion-induced secondary electron yield is very similar in all the studied cases; the yield range, however, is consistently larger for helium than for gallium, which partially explains the enhanced topographical contrast of helium microscopes over the gallium focused ion beams.

FIB
secondary emission
angular dependency
image formation
He microscope

http://resolver.tudelft.nl/uuid:da1a57c4-9005-4d78-bc78-d12e77ffaa42

https://doi.org/10.1017/S1431927611000225

Cambridge University Press

2012-06-16

1431-9276

Microscopy and Microanalysis, June 16, 2011

Institutional Repository

journal article

(c) 2011 Castaldo, V.
Withagen, J.
Hagen, C.
Kruit, P.
Van Veldhoven, E.
Microscopy Society of America