Resolution estimation of low electron energy probe lens system

To estimate the resolution of the SEM with an aberration corrector, some electron optical systems having multipole lenses are analyzed up to the seventh order using Lie algebra and differential algebra. It is shown that the high order combination aberrations can be decreased to less than 15 if the transfer lens system or retarding voltage system is applied. The systematic correction method of aperture aberration is described up to the fifth order or more. The resolution better than 0.3–0.5 nm may be obtained at 1 keV beam energy using the correction devices.