Pulsed TOF-SIMS in a Helium Ion Microscope

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their enormous lateral resolution of below 0.3 nm and the highest 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. In the present contribution we will present a new and relatively easy to implement time of flight method for Ion Beam Analysis (IBA) in the HIM. We utilize pulsed time of flight spectrometry to obtain elemental information from the sample. We will show initial results demonstrating the flexibility and applicability of the method to image samples with target mass contrast and analyze the target compositions. 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 ions. This has been achieved by chopping the primary ion beam down to pulse widths of 5.5 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. The focus of the contribution will be on the TOF-SIMS concept. SIMS complements the RBS in a way that lateral resolved TOF-SIMS would enable fast qualitative elemental identification and contrast where the TOF-RBS serves quantitative sample compositions free from standards. In addition we point out mayor challenges, downsides and physical limitation of IBA in the HIM.
[1] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema, J. Vac. Sci. Technol. B 32(2), 2014