Dopant contrast in the helium ion microscope

Due to miniaturisation of semiconductor devices, there is an increasing need for nanoscale characterisation of dopant distributions. Scanning electron microscopy (SEM) has been identified as a potential technique to fulfil this need, providing that a small enough probe size (~ 0.1 nm) could be achieved. Probes of this size are not possible in a low-voltage scanning electron microscope but a He-ion beam can be focussed to probe sizes as small as 0.25 nm; a significant improvement over that attainable in the SEM. This paper presents results from the first use of helium ion microscopy (HeIM) to examine dopant contrast in semiconductor materials. It was found that the spatial resolution is improved when compared to SEM and that the contrast mechanism has similarities making HeIM an ideal candidate for future 2-dimensional nanoscale dopant mapping.