Immersion Objective with Improved Focusing

Abstract A theoretical possibility of improving the focusing quality of electron beams in an immersion objective by taking into account spherochromatic aberrations of the third order is considered. In this case, the resolution of the immersion objective is increased by reducing its total aberration by mutual correction of spherochromatic aberrations of the second and third orders. It is shown that when taking into account spherochromatic aberrations up to and including the third order and statistical regularities of electron emission, the radius of the electron beam scattering circle in the plane of the Gaussian image of the immersion objective decreases by almost an order of magnitude (by 6.75 times) and, accordingly, its resolution increases by the same amount. For the first time, focusing properties of a three-electrode immersion objective consisting of a flat cathode and two coaxial cylinders of equal diameter separated by gaps of finite width have been calculated taking into account spherochromatic aberrations up to and including the third order and statistical regularities of electron emission. In this case, the ratios between the sizes of the electrodes of the immersion objective and potentials on them are consistent with the parameters of electron emission.