Electron probe apparatus using an electrostatic field to cause secondary electrons to diverge

Claim 2

Electron beam apparatus comprising means for generating a high energy beam of electrons, a specimen stage in the path of said beam, designed to receive a specimen for impingement thereon of said beam, and means for detecting secondary electrons emitted by and diverging from said specimen as a consequence of said impingement, wherein the improvement lies in the provision of guiding means for controlling the path of said secondary electrons from the specimen to the detecting means, said guiding means comprising an electrode structure creating a divergent electrostatic field in the path of said secondary electrons from said specimen, said field being selected to cause said secondary electrons of a given energy and following different paths from said specimen to spread out to a greater degree than they would do in the absence of said field thereby increasing the mutual divergence of said paths so as to accentuate differences in the trajectories of said secondary electrons, said detecting means occupying only a fraction of the solid angle over which the secondary electrons which are subjected to the increased divergence are spread.

Claim 3

The electron beam apparatus of claim 1 wherein said guiding means comprise a hollow cylindrical shield, said shield being disposed with the axis thereof substantially normal to the surface of said specimen at the point of impingement of said beam.

Claim 4

The electron beam apparatus of claim 2 wherein said secondary electron detecting means are disposed in the wall of said shield occupying only a fraction of the surface area thereof.

Claim 5

The electron beam apparatus of claim 2 wherein said shield is at an electric potential which is positive with respect to said specimen.

Claim 6

The electron bean apparatus of claim 2 wherein said shield has a diameter greater than the axial length thereof.

Claim 7

The electron beam apparatus of claim 2 wherein said guiding means further comprise a disc-shaped electrode, said electrode being disposed with its axis coincident with the axis of said shield and being disposed at the opposite end of said shield from said specimen.

Claim 8

The electron beam apparatus of claim 6 wherein said electrode is at the same potential as said specimen.

Claim 9

Electron beam apparatus comprising means for generating a beam of electrons, a specimen stage designed to receive a specimen for impingement thereon of said beam, means for detecting secondary electrons emitted by said specimen as a consequence of said impingement and guiding means for said secondary electrons, said guiding means creating a divergent electrostatic field in the path of said secondary electrons from said specimen such as to cause said secondary electrons of a given energy to spread out, accentuating differences in the trajectories thereof, said guiding means comprising first a hollow cylindrical shield, said shield being disposed with the axis thereof substantially normal to the surface of said specimen at the point of impingement of said beam, seconDly a disc-shaped electrode disposed with its axis coincident with the axis of said shield and at the opposite end of said shield from said specimen, and thirdly a ring-shaped electrode adjacent said shield and between said shield and said specimen, said ring-shaped electrode being at an electric potential which is negative with respect to said specimen whereas said first-mentioned disc-shaped electrode and said shield are at the same potential as said specimen, said means for detecting secondary electrons being disposed in the wall of said shield and occupying only a fraction of the surface area thereof.

Claim 10

Electron beam apparatus comprising means for generating a beam of electrons, a specimen stage designed to receive a specimen for impingement thereon of said beam, means for detecting secondary electrons emitted by said specimen as a consequence of said impingement and guiding means for said secondary electrons, said guiding means creating a divergent electrostatic field in the path of said secondary electrons from said specimen such as to cause said secondary electrons of a given energy to spread out, accentuating differences in the trajectories thereof, said guiding means comprising first a hollow cylindrical shield, said shield being disposed with the axis thereof substantially normal to the surface of said specimen at the point of impingement of said beam, seconDly a disc-shaped electrode disposed with its axis coincident with the axis of said shield and at the opposite end of said shield from said specimen, and thirdly a ring-shaped electrode adjacent said shield and between said shield and said specimen, said ring-shaped electrode being at an electric potential which is negative with respect to said specimen whereas said first-mentioned disc-shaped electrode and said shield are at the same potential as said specimen, said means for detecting secondary electrons being disposed in the wall of said shield and occupying only a fraction of the surface area thereof.