Scanning electron beam apparatus for viewing potential distribution on specimen surfaces

Claim 1

Electron beam apparatus comprising electron gun means for forming a high-energy probe of electrons having an energy of the order of thousands of electron volts, lens means focusing said probe, a specimen having a surface thereof in the path of said probe for impact thereon of said probe, a detector adapted to receive secondary electrons emerging from said specimen surface as a consequence of the impact thereon of said probe said detector subtending a restricted solid angle at said specimen surface, image display means connected to said detector to receive signals therefrom generated by said secondary electrons, deflection means acting on said probe to deflect said probe laterally, said image display means being synchronized with said deflection means such as to produce an image of a region of said specimen surface in terms of said secondary electrons, a first grid between said specimen surface and said detector, said first grid being at a substantial positive electric potential with respect to said specimen, such as to create a voltage gradient between said first grid and specimen surface which is not less than 5,000 volts per meter, and said potential being not less than 25 volts, a second grid between said first grid and said detector, said second grid being at a potential which is negative and low but variable with respect to the specimen, the potential of said second grid being of the order of between zero and -5 volts.