Helium Ion Microscopy: a New Technique for Semiconductor Metrology and Nanotechnology

Abstract

The Helium Ion Microscope (HIM) offers a new, potentially disruptive technique for nano‐metrology. This methodology presents an approach to measurements for nanotechnology and nano‐manufacturing which has several potential advantages over the traditional scanning electron microscope (SEM) currently in use in integrated circuit research and manufacturing facilities across the world. Due to the very small, essentially one atom size, very high brightness source, and the shorter wavelength of the helium ions, it is theoretically possible to focus the ion beam into a smaller probe size relative to that of an electron beam of current SEMs. Hence higher resolution is theoretically achievable. In contrast to the SEM, when the helium ion beam interacts with the sample, it generates significantly smaller excitation volume and thus the image collected is more surface sensitive. Similarly to the SEM, the HIM also produces topographic, material, crystallographic, and potential contrast, and offers ways for investigating new properties of the sample through the use of various detectors. Compared to an SEM, the secondary electron yield is quite high, allowing for imaging at very low beam currents, thus resulting in less sample damage. Additionally, due to their low mass, the helium ions themselves do not significantly alter the sample, which would be common, for example, for gallium ions that are regularly used for ion milling. This paper reports on some of the preliminary work being done at NIST in the exploration of HIM as a measurement tool for nano‐metrology.