Temperature Dependent Electron Emission in Focused Ion Beam Microscopes

Transistors in mass produced consumer electronics have characteristic dimensions on the nanometer scale, with companies such as Intel and Samsung continuously working to increase transistor density by fabricating smaller components. Thermal management (i.e., temperature during use) plays a key role in effective operation of these devices. However, measuring temperature of nanometer scale components presents a challenge. Optical techniques commonly used in failure analysis, such as IR thermography, are diffraction limited and cannot effectively access the nanoscale. Contact techniques such as scanning thermal microscopy offer nanoscale resolution, but parasitic losses from the scanning tip limit temperature sensitivity. Transmission electron microscopy has been used to demonstrate thermal effects with nanometer resolution but can only accommodate devices that have been thinned to ~100 nm. Scanning electron microscopy shows some promise as a noncontact technique that has topographical resolution of ~1 nm and has shown preliminarily to have temperature dependence in secondary electron counts.<br/><br/>Here we examine thermal effects in Focused Ion Beam (FIB) microscopes. FIB microscopes offer several advantages over using a single beam SEM instrument: (1) the ion beam does not generate backscattered electrons, improving signal to noise ratio, (2) the ion beam can mill samples, allowing measurements of subsurface features in devices without breaking vacuum, and (3) FIB tools are almost exclusively manufactured as dual beam FIB-SEMs, so electron beams are simultaneously accessible. Using the FIB-SEM we demonstrate temperature dependence in grayscale intensity in semiconductor images. We additionally show results of energy mapping at different temperatures at multiple temperatures using the through lens detector built into FIB-SEM microscopes. Comparison of temperature dependent effects in SEM and FIB images are discussed. We also examine the additional considerations of accelerating voltage, power normalization, ion implantation, and spatial resolution.<br/><br/><i>Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.</i>