Helium ion microscopy and its application to nanotechnology and nanometrology

Helium ion microscopy (HeIM) presents a new approach to nanotechnology and nanometrology, which has several potential advantages over the traditional scanning electron microscope (SEM) currently in use in research laboratories and manufacturing facilities across the world. Owing to the very high source brightness, and the shorter wavelength of the helium (He) ions, it is theoretically possible to focus the ion beam into a smaller probe size relative to that of the electron beam of an SEM. Hence, resolution 2 × – 4 × better than that of comparable SEMs is theoretically possible. In an SEM, an electron beam interacts with the sample and an array of signals are generated, collected and imaged. This interaction zone may be quite large depending upon the accelerating voltage and materials involved. Conversely, the helium ion beam interacts with the sample, but it does not have as large an excitation volume and, thus, the image collected is more surface sensitive and can potentially provide sharp images on a wide range of materials. Compared with an SEM, the secondary electron yield is quite high—allowing for imaging at extremely low beam currents and the relatively low mass of the helium ion, in contrast to other ion sources such as gallium, potentially results in minimal damage to the sample. This article reports on some of the preliminary work being done on the HeIM as a research and measurement tool for nanotechnology and nanometrology being done at NIST. SCANNING 30: 457–462, 2008. Published 2008 by Wiley Periodicals, Inc.