Method and apparatus for automatic focusing of scanning electron

Details Method and apparatus for automatic focusing of scanning electron Method and apparatus for automatic focusing of scanning electron

1991-07-17

1992-07-14

Berman, Jack I.

Radiant energy

Inspection of solids or liquids by charged particles

Electron probe type

250307, 250396R, 250396ML, 250397, H01J 3721

Patent

active

051305402

ABSTRACT:
Method and an apparatus for automatically moving the focal plane of the electron beam produced by a scanning electron microscope to the position of specimen surface. An auxiliary coreless coil of a low inductance is disposed close to the objective lens. The exciting current fed to the coil is varied to move the focal plane of the electron beam toward the optical axis. At each of discrete positions of the focal plane, a specimen is scanned with the electron beam. The resulting secondary electrons are detected by a detector. Individual output signals from the detector are compared to select the maximum signal. Then, only the objective lens is excited. The exciting current fed to the objective lens is modified to move the focal plane along the position closest to the specimen surface.

REFERENCES:
patent: 4199681 (1980-04-01), Namae

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