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Aberration Corrector and Method of Aberration Correction

  • US 20080093563A1
  • Filed: 10/18/2007
  • Published: 04/24/2008
  • Est. Priority Date: 10/20/2006
  • Status: Abandoned Application
First Claim
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1. An aberration corrector for correcting aberration produced in a lens disposed in the direction of motion of a spreading electron beam which is cylindrically symmetrical, said aberration corrector comprising:

  • a first quadrupole field-producing multipole element on which the electron beam not yet corrected for the aberration impinges, the first quadrupole field-producing multipole element producing a first quadrupole field; and

    a second quadrupole field-producing multipole element from which the electron beam corrected for the aberration exits, the second quadrupole field-producing multipole element producing a second quadrupole field,wherein each of said first and second quadrupole fields produces an optical system having a two-fold astigmatic effect of a primary term of the quadrupole field and a focusing effect in the direction of divergence of a cylindrically symmetrical type, said focusing effect being produced by higher-order terms of the quadrupole field which have magnitudes increasing at higher rates than the primary term when the length in the direction of motion of the electron beam is increased, andwherein said first and second quadrupole fields are set to mutually opposite polarities, whereby the two-fold astigmatic effects of the first and second quadrupole fields on the cylindrically symmetrical electron beam having the spread are canceled out and only the focusing effect in the direction of divergence of the cylindrically symmetrical type is used for correction of the aberration in the lens.

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