Abstract: An imaging symmetrical energy filter (of the .OMEGA.-type) comprising two pairs of sector magnets (1), (2), (3), (4) for an electron microscope. The second-order chromatic aberration is corrected by arranging the two pairs of sector magnets {(1),(4) and (2),(3)} further apart. This enables suitable arrangement of the coils to generate correction hexapole fields, so that the chromatic error is even completely eliminated. Moreover, correction of the third-order aperture aberration is also possible by constructing the hexapole coil (9) in the symmetry plane also as an octupole coil. Further correction of this third-order aberration is achieved by applying an octupole field (5) directly at the entrance of the first sector magnet (1) and an octupole field (13) directly at the exit of the fourth sector magnet (4).

Abstract: A charged particle beam system utilizes a box-shaped cooling member accommodating the lens in order to cool the particle-optical lenses. The cooling medium is circulated between the wall of the lens and the wall of the cooling member, enabling a high transfer of heat by convection. By using a cooling liquid which is undersaturated for air and which is heated prior to its passage through the cooling duct, accumulation of air due to heating can be prevented in the cooling member.

Abstract: For the selection of a pure electron beam or ion beam from a mixed beam, use is made of a combined electrostatic/magnetic deflection system, the electrostatic deflection system being formed, for example, by a tilted electrode system of a cascade system of electrodes present in the apparatus. The pure beam is directed onto an object to be irradiated as near to the object as possible in order to prevent renewed mixing.

Abstract: By using, in beam path correction, a three-point adjustment of the beam wobbler, the beam path can be optimized for realizing minimum picture errors in the apparatus. For different lens energizations a picture-shifting correction can simply be carried out dynamically.