Patent ID: 8063365

Claim:
An electron gun for an electron beam lithography tool or an electron beam inspection tool, the electron gun comprising: a cathode configured to emit electrons; a Wehnelt electrode to form an electron cloud at an emitting region near the cathode; an anode configured to accelerate the electrons so as to create an electron beam, wherein the Wehnelt electrode and the anode together act to form a first cross-over between the emitting region and the anode within the electron gun and to form a first cathode image within the electron gun; a first electron lens configured to focus the electron beam to form a second cross-over within the electron gun and a second cathode image at an intermediate image plane within the electron gun; a beam aperture positioned at an exit of the electron gun; a second electron lens configured to focus the electron beam to form a third cross-over within the electron gun and a third cathode image at the beam aperture, wherein there are no beam apertures in the electron gun that are positioned at non-focal planes.