Apparatus and methods for aberration correction in electron beam based system

A method of correcting aberration in electron-optics of an electron beam system, the method comprising:

• adjusting an inner voltage level applied to an inner electrode surrounding an opening or reflector, the inner electrode having a continuous annular planar surface in a plane of the opening or reflector;
• and
• adjusting at least one outer voltage level which is applied to at least one outer electrode around the inner electrode, the at least one outer electrode having a planar surface in the plane of the opening or reflector,
• wherein the inner voltage level and the at least one outer voltage levels, as applied to said electrodes, each causes an electric field that influences both electrons incident to the opening or reflector and electrons outgoing from the opening or reflector.

An electron beam column comprising:

• an electron source for generating an electron beam that travels along an optical axis of the electron beam column;
• condenser electron-optics in the electron beam column for focusing and collimating the electron beam;
• an inner electrode in the electron beam column that is positioned in a pupil plane of the electron beam column and has a continuous annular shape surrounding an opening through which the electron beam is transmitted, wherein the optical axis is normal to the pupil plane;
• at least one outer electrode positioned in the pupil plane so as to surround the inner electrode;
• and
• circuitry configured to apply an inner voltage level to the inner electrode and at least one outer voltage level to the at least one outer electrode.