Deflection beam-chopping in the SEM

Abstract

Beam-chopping in the scanning electron microscope (SEM) by electrostatic deflection over an aperture is examined in some detail. The chopping aperture used is the final aperture image and the beam is of finite diameter. The required deflection angle to cut off the beam and the apparent movement of the spot due to the deflection in chopping are obtained for the cases of the deflection structure placed between the gun and the top lens and between the gun and the other lens.