Patent ID: 8178850

Claim:
A chromatic aberration corrector for use with a charged-particle beam system using a charged-particle beam having an optical axis, said chromatic aberration corrector comprising: a first multipole element having a first thickness along the optical axis of the charged-particle beam and producing a first static electromagnetic field of 2-fold symmetry; and a second multipole element mounted on the optical axis, having a second thickness along the optical axis, and producing a second static electromagnetic field of 2-fold symmetry, wherein when the charged-particle beam is accelerated by a given accelerating voltage, the first and second static electromagnetic fields cancel out 2-fold astigmatism in the charged-particle beam while satisfying a condition given by 2 ⁢ f 2 t 2 ≧  A e ⁢ ⁢ 2 - A m ⁢ ⁢ 2  where A e2 is the amount of 2-fold astigmatism per unit length produced by an electric field quadrupole, A m2 is the amount of 2-fold astigmatism per unit length produced by a magnetic field quadrupole, t is the length (thickness) of each multipole element taken in the direction of the beam, and f is the focal distance of an objective lens, wherein chromatic and spherical aberrations are corrected simultaneously by superimposing a static electric or magnetic field of 3-fold symmetry on said first multipole element and superimposing a static electric or magnetic field of 3-fold symmetry on said second multipole element.