Measurement of the profile of finely focused electron beams in a scanning electron microscope

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Abstract
Electron beam spot diameters can be estimated either by resolution tests or by scanning the beam over a sharp edge and detecting the transmitted (or reflected) current. The sharp edge method can yield quantitative information about the beam profile, but the resolution is usually limited to tens of nanometres because of the difficulty of providing a suitably straight, opaque edge. A method is described whereby vertical etched silicon edges can be used to provide reliable and consistent measurements of beam diameters. The resolution limit depends on various factors described, but is usually better than 5 nm. The use of the method for manual or automatic astigmatism correction is also discussed.