Patent ID: 7723683

Claim:
An aberration correction system for use in an electron microscope, said aberration correction system comprising: three stages of multipole elements arranged in a row along an optical axis, each of the multipole elements having a thickness along the optical axis, the three stages of multipole elements including a front stage of multipole element, a middle stage of multipole element, and a rear stage of multipole element, wherein said front stage of multipole element produces a first magnetic or electric field of 3-fold symmetry with respect to the optical axis, wherein said middle stage of multipole element produces a second magnetic or electric field of 3-fold symmetry with respect to the optical axis, wherein said rear stage of multipole element produces a third magnetic or electric field of 3-fold symmetry with respect to the optical axis, wherein in the second magnetic or electric field, a distribution of a magnetic or electric field of 3-fold symmetry is created in a direction not to cancel out an astigmatism of 3-fold symmetry produced from the first magnetic or electric field or from the third magnetic or electric field, wherein in the third magnetic or electric field, a distribution of a magnetic or electric field of 3-fold symmetry is created in a direction not to cancel out an astigmatism of 3-fold symmetry produced from the first magnetic or electric field or from the second magnetic or electric field, wherein an aberration of 3-fold symmetry produced in the front stage of multipole element is rotated using the middle stage of multipole element, wherein an aberration of 3-fold symmetry produced from the middle stage of multipole element is rotated using the rear stage of multipole element, and wherein the astigmatisms of 3-fold symmetry are canceled out by combining the fields produced by the three stages of multipole elements, whereby spherical aberration and a higher-order aberration are corrected.