US 6,888,145 B2Granted

Optical particle corrector

AssigneeCEOS Corrected Electron Optical Systems GmbH

InventorsHeiko Müller, Harald Rose

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Abstract

An optical particle corrector with a straight optical axis for eliminating color and aperture aberrations in optical particle lenses includes multipole elements in the form of electric and/or magnetic quadrupole and octupole elements. There are at least twelve quadrupole elements and ten octupole elements, in which three quadrupole elements and two octupole elements are assembled into a group. These groups are arranged successively along the straight optical axis, in which a first symmetrical plane is defined between the first and second groups, a second symmetrical plane is defined between the second and third groups and a third symmetrical plane is defined between the third and fourth groups. The multipole elements from one group to another correspond to each other in pairs, in which the multipole elements of the corresponding following group are positioned in reverse order along the straight optical axis in comparison with the corresponding multipole elements of the preceding group. The structure and refractive powers of the multipole elements that correspond to each other are mirror-symmetrically configured relative to the corresponding symmetrical plane between the groups. At least two of the quadrupole elements generate electric-magnetic quadrupole fields, in which the quadrupole element are, preferably, arranged in a mirror-symmetrical manner relative to the second, or to all, symmetrical planes. An additional octupole element is arranged in the first and third symmetrical planes. The corrector enables the transmission of extremely large image fields, while the optical quality remains the same due to the fact image aberrations outside the axis can be corrected.

A particle optical corrector having multipole elements in the form of electrical quadrupole or magnetic quadrupole elements and octupole elements for eliminating chromatic aberration and spherical aberration of particle optical lenses, said particle optical corrector comprising:

at least twelve quadrupole elements (Q1-Q3′″) and ten octupole elements (O1-O4) with three quadrupole elements of said twelve quadrupole elements and two octupole elements of said ten octupole elements forming a group of elements (G) with a plurality of groups of elements (G1-G4) being arranged one group behind another group along a straight optical axis;
said multipole elements from said group of elements to said group of elements corresponding to one another in pairs (Q1 and Q1′;
Q2 and Q2′;
Q3 and Q3′) and said multipole elements (Q3′, Q2′, Q1′) of a respective following said group of elements being positioned in reverse sequence along said straight optical axis to corresponding said multipole elements (Q1, Q2, Q3) or a respective preceding said group of elements;
the respective mutually corresponding multipole elements (Q1, Q1′, Q1″, Q1′″;
O1, O1′, O1″, O1′″) are mirror symmetrical to respective center planes between each said group of elements, with said center plane between a first group of elements and a second group of elements defining a first plane of symmetry, said center plane between said second group of elements and a third group of elements defining a second plane of symmetry, said center plane between said third group of elements and a fourth group of elements defining a third plane of symmetry;
at least two quadrupole elements of said at least twelve quadrupole elements generating an electrical quadrupole field and a magnetic quadrupole field and said at least two quadrupole elements being arranged mirror symmetrically to at least said second plane of symmetry;
and,
an additional octupole element being provided in said first plane of symmetry and said third plane of symmetry.

6 more elements

Abstract

Claims20