Charged particle beam apparatus and aberration corrector

Abstract

High expectations are placed on aberration correctors to increase the resolving power of charged particle devices. Meanwhile, a far more complicated configuration and higher mechanical precision assembly in comparison to prior art aberration correctors are necessary in charged particle beam optical devices that use low-energy electron beams. A complex electromagnetic quadrupole part employed in the aberration corrector preferably has the forward extremities of the poles provided in a vacuum near an electron beam path and excitation coils disposed outside the vacuum, and this necessitates a structure that can achieve both electrical insulation and vacuum sealing for each of these poles. Such structural complexity generally conflicts with improving mechanical assembly precision. The complicated structure in the above problems can be simplified by: separating the electrodes and the magnetic poles in the complex electromagnetic multipole that had been used in prior art aberration correctors; and offsetting the positions of both, or ensuring that the widths of both do not match. Consequently, improvement of mechanical assembly precision can be achieved.