A method for improving the resolution of a scanning electron microscope (SEM) designed for inspection of
nanodevices was developed. The trade-off between the resolution and depth of focus of the SEM was quantitatively
evaluated by a method based on "information passing capacity". It was theoretically and experimentally shown that
depth of focus is enhanced under observation conditions with increased pixel size. Furthermore, increasing depth of
focus is effective in obtaining high-resolution images because increasing the pixel size of the formed SEM image
maintained the focal plane of the electron beam. The maximum axial magnetic field and the focal length of the objective
lens in the SEM optics needed to obtain a resolution of 0.9 nm were determined theoretically. The maximum axial
magnetic field can be strengthened by improving the immersion lens in the SEM optics in terms of geometry and
material composition. The focal length was reduced by adopting the immersion lens and by dynamically controlling the
electron beam by deflectors as well as optical correctors. This method will be applied in developing apparatuses for
R&D purposes as well as for improving the yield of the production process for integrated circuits.
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