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

Published online by Cambridge University Press:  16 June 2011

Vincenzo Castaldo ,
Josephus Withagen ,
Cornelius Hagen ,
Pieter Kruit  and
Emile van Veldhoven
Vincenzo Castaldo*
Affiliation:
Department of Applied Science, Delft University of Technology, Lorentzweg 1, Delft, Zuid-holland 2628CJ, The Netherlands
Josephus Withagen
Affiliation:
Department of Applied Science, Delft University of Technology, Lorentzweg 1, Delft, Zuid-holland 2628CJ, The Netherlands
Cornelius Hagen
Affiliation:
Department of Applied Science, Delft University of Technology, Lorentzweg 1, Delft, Zuid-holland 2628CJ, The Netherlands
Pieter Kruit
Affiliation:
Department of Applied Science, Delft University of Technology, Lorentzweg 1, Delft, Zuid-holland 2628CJ, The Netherlands
Emile van Veldhoven
Affiliation:
TNO Science and Industry, Stieltjesweg 1, Delft, Zuid-holland 2628CK, The Netherlands
*
Corresponding author. E-mail: vinc.castaldo@gmail.com
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Abstract

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.

Keywords

FIBsecondary emissionangular dependencyimage formationHe microscope
Type
Helium Ion Microscopy
Information
Microscopy and Microanalysis , Volume 17 , Issue 4 , August 2011 , pp. 624 - 636
Copyright
Copyright © Microscopy Society of America 2011

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References

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