IBA on a Nanometer Scale by use of a Helium Ion Microscope - Challenges, Achievements and ongoing Progress

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their enormous lateral resolution of about 0.3 nm and the ultimate field of depth make them a unique tool in surface imaging. The imaging contrast in such devices is usually generated either by measuring the secondary electron emission yield (SE mode) or the backscattered He ion yield (RBI mode). So far there is no possibility to analyze target compositions (elements) in a quantitative manner.
In the present contribution we will show concepts as well as first preliminary studies on the capability, efficiency and the limits of applying (Rutherford) Backscattering Spectrometry (RBS) within a HIM device to image samples with target mass contrast and to analyze target compositions. In particular, the capability of different kind of particle detectors (Si detector, TOF-setup, electrostatic and magnetic analyzers) with respect to their use for IBA in a HIM will be discussed.
The basic considerations and design studies are accompanied by first He backscat- tering investigations for energies between 1-40 keV using a test facility equipped alternatively with a time-of-flight detector or a classical 70° ESA. For various projectile energies the energy resolution of both detection systems is measured and compared to theoretical estimations. Moreover, we will present an experimental setup which allows to perform quantitative measurements on the secondary electron yield, the absolute backscattering cross sections and the charge fraction of the backscattered particles for ions with low energies in the order from sub keV to 40 keV. These measurements will be one key point on the way to a quantitative IBA within the HIM.