Beam Size in A High-Resolution Ion Microprobe Operated at High Current

Abstract

In recent years the development of liquid metal ion (LMI) sources has made it possible to produce high intensity focused ion beams - beams with current densities of the order of a few amperes per square centimeter and diameters of from less than 50 nanometers to a few micrometers [1,2]. These beams have been applied in areas such as scanning ion microscopy, surface analysis, lithography, implantation and micromachining (removing minute amounts of material in a precise and programmed way). In terms of technological utility micromachining has been the most important of these applications and dozens of focused ion beam systems are in use around the world, for failure analysis and circuit modification. These latter applications depend on the ion beam for removing minute amounts of material from a surface, inspecting the modified surface and for decomposing metal-bearing gases so as to deposit conducting runs on circuits.Some of the features of LMI sources that make them so useful for focused beams are: a high angular intensity of 20 microamperes/steradian, typically [3]; a small apparent source size δ of roughly 50 nanometers [4,5]; wide variety of ionic species including Ga, In, Be, Au, Si, As and B (the latter five species requiring a mass-filtering focusing column); great compactness and extremely reliable operation.