On the resolution of semiconductor multilayers with a scanning electron microscope

The main factors affecting the spatial resolution of the scanning electron microscope have been analysed using a suitable inhomogeneous specimen consisting of semiconductor multilayers. Operating in secondary electron as well as in backscattered electron imaging mode, with the support of Monte Carlo simulations of beam-specimen interaction, it has been possible to achieve the following conclusions. All the backscattered or secondary electrons positively contribute to the image formation independently of their trajectories and specimen exit points. The resolution of the backscattered electron images depends only on the beam size and the signal to noise ratio. The generation volume of backscattered electrons affects the contrast but does not represent in itself a limit to the resolution. The contrast of secondary electron images of the semiconductor multilayer has essentially a compositional nature, being linked to the collection of secondary electrons produced by the backscattered ones. Moreover, using a converter of backscattered electrons in secondary electrons located underneath the pole pieces of the microscope objective lens, it has been demonstrated an improvement of the signal that allows a resolution equal to the electron beam size. This resolution cannot be obtained, operating in the same electron optical conditions, without the converter, due to the lower signal level.