| 摘要 |
The present invention addresses the problem that an electromagnetic lens for a charged particle beam exerts a positive spherical aberration, and that correcting this spherical aberration requires a complex combination of electromagnetic lenses. In the present invention, one among a circular aperture and an annular aperture is formed in an entry plate disposed on a charged particle beam entry side, the other among the circular aperture and the annular aperture is formed in a plate disposed on the exit side, and a voltage is applied between the entry plate and an exit plate. Then, an electric field formed in the annular aperture exerts divergence whereby the positive spherical aberration is canceled. The present invention allows the spherical aberration to be corrected with an extremely simple and readily achievable structure. |
