| 摘要 |
The invention concerns a corrector (9) for chromatic and aperture aberration correction in an electron microscope with six multipoles (1, 2, 3, 4, 5, 6) which are disposed in the optical path (7) one after the other symmetrically with respect to a symmetry plane (8) for generating quadrupole fields (1′, 2′, 3′, 4′, 5′, 6′) and octupole fields, wherein the quadrupole fields (1′, 2′, 3′, 4′, 5′, 6′) of all six multipoles (1, 2, 3, 4, 5, 6) are consecutively rotated through 90° with respect to one another, thereby generating a mirror-symmetrical exchange symmetry of the axial fundamental rays (xα, yβ). In accordance with the invention, the following is provided for correcting azimuthal coma: A double multipole (10) with a multipole element (11) upstream of the symmetry plane (8) and a multipole element (12) downstream of the symmetry plane (8), which generates two octupole fields (11′, 12′) of the same orientation as the quadrupole fields (1′, 2′, 3′, 4′, 5′, 6′) and two further octupole fields (11″, 12″), which have opposite poles and exert a force on the electrons in a direction rotated through 90° with respect to the above-mentioned octupole fields (11′, 12′) in the principal sections (x, y). The six multipoles (1, 2, 3, 4, 5, 6) generate octupole fields (1″, 2″, 3″, 4″, 5″, 6″) with the same orientation, and the adjustment of the poles and of the field strengths of the octupole fields (1″, 2″, 3″, 4″, 5″, 6″, 1″, 12″) is used for the above-mentioned correction.
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