Developments in low‐voltage microscopy instrumentation

Abstract

Low-voltage microscopy can produce high-resolution, high-contrast images of nanometer-scale surface features. Several techniques exist for low-energy electron generation, but most successful in current instrumentation is the combination of a magnetic lens with an electrostatic immersion lens. This compound lens allows the low-voltage column to maintain high potential in the column while independently controlling the landing energy on the sample. Aberration coefficients decrease linearly with the immersion ratio leading to larger optimum semiconvergent angle on the sample and improvement in spot size and beam current. Most recently highly scaled miniature electron beam columns have shown promising low-voltage performance from all electrostatic lenses operating only at low potential. This article explores the current design of low-voltage columns, including variations on compound lenses and miniature lenses, and from a system level, discusses the strength and weaknesses of each design.