Monte Carlo simulations of secondary electron emission due to ion beam milling

Abstract

The authors present a Monte Carlo simulation study of secondary electron (SE) emission resulting from focused ion beam milling of a copper target. The basis of this study is a simulation code which simulates ion induced excitation and emission of secondary electrons, in addition to simulating focused ion beam sputtering and milling. This combination of features permits the simulation of the interaction between secondary electron emission, and the evolving target geometry as the ion beam sputters material. Previous ion induced SE Monte Carlo simulation methods have been restricted to predefined target geometries, while the dynamic target in the presented simulations makes this study relevant to image formation in ion microscopy, and chemically assisted ion beam etching, where the relationship between sputtering, and its effects on secondary electron emission, is important. The authors focus on a copper target and validate the simulation method against experimental data for a range of noble gas ions, ion energies, ion/substrate angles, and the energy distribution of the secondary electrons. The authors then provide a detailed account of the emission of secondary electrons resulting from ion beam milling; the authors quantify both the evolution of the yield as high aspect ratio valleys are milled, as well as the emission of electrons within these valleys that do not escape the target, but which are important to the secondary electron contribution to chemically assisted ion induced etching.