Patent ID: 8895922
Filing Date: 2014-11-25
Classification: G21K,H01J

Abstract:
1. A method suitable for preparing a specimen for inspection, the method comprising the steps of: irradiating a photocathode which is configured to be aspheric so that the photocathode emits electrons from a surface of the photocathode, wherein the emitted electrons follow a plurality of different trajectories, and the plurality of trajectories of the electrons are such that they can be extrapolated to intersect at a plurality of different regions within the photocathode, the plurality of different regions defining a plurality of virtual sources located within the photocathode which is configured to be aspheric, and wherein the photocathode comprises an aspheric rounded tip which has more than one radius of curvature; configuring the emitted electrons so that they form an electron beam; focusing the electron beam onto a specimen to form images of the plurality of virtual sources on the specimen, wherein each of the plurality of virtual sources is positioned so as to compensate for optical aberration such that images of each of the plurality of virtual sources are located within a selected predefined region on the specimen so that the predefined region is irradiated.