Nanometer TOF-RBS and TOF-SIMS in a Helium/Neon Ion Microscope

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their excellent lateral resolution down to 0.3 nm and their high field of depth make them a unique tool in surface imaging [1]. So far the possibilities to identify target materials (elements) are rather limited or need complex detection setups.
We will present a new and relatively easy to implement method for ion beam analysis in the HIM by means of time of flight spectrometry to obtain elemental information from the sample. We will demonstrate the flexibility and applicability of the method to image samples with target mass contrast, to analyze the target compositions, and to measure depth profiles of films with few tens of nm thickness.
Pulsing the primary helium or neon ion beam and measuring the time of flight of secondary particles from the sample allows to obtain the energy of the backscattered particles or the mass of the sputtered target atoms (and ions). This has been achieved by chopping the primary ion beam down to pulse widths of 18 ns by use of the built in beam blanker and a customized plug-on beam blanking electronics. The secondary particles are detected by means of a multi channel plate mounted on a flange of the HIM.
We will show TOF-RBS and TOF-SIMS measurements for different materials which can give complementary information. Lateral resolved TOF-SIMS allows to quickly obtain qualitative elemental mapping while the TOF-RBS gives the standard-free quantitative sample composition of regions of interest. We will also show, that with TOF-RBS depth profiling of nm-thick layers is possible. In addition we will discuss major challenges and physical limitations of ion beam analysis in the HIM.
[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014