| 摘要 |
<p>An aberration corrector is offered which simultaneously corrects chromatic aberration and spherical aberration in a charged particle beam (17). The corrector has two stages of multipole elements (12, 13) each of which has a thickness along the optical axis (11). Eachmultipole element (12, 13) produces a static electric or magnetic field of 3-fold symmetry and a static electromagnetic field of 2- or 3-fold symmetry superimposed on the static electric or magnetic field. In each of the multipole elements (12, 13), the static electromagnetic field is so set that magnetic and electric deflecting forces on an electron beam (17) accelerated by a given accelerating voltage substantially cancel out each other. Thus, chromatic aberration is corrected. Also, spherical aberration is corrected by the static electric or magnetic fields of 3-fold symmetry produced by the multipole elements (12, 13).
</p> |
