Electrooptical viewing apparatus capable of switching depth of f

Details Electrooptical viewing apparatus capable of switching depth of f Electrooptical viewing apparatus capable of switching depth of f

1992-05-21

1993-07-06

Anderson, Bruce C.

Radiant energy

Inspection of solids or liquids by charged particles

Electron microscope type

250356R, 250398, H01J 3710

Patent

active

052256766

ABSTRACT:
An electron microscope capable of switching its depth-of-focus mode between a first and a second mode. The microscope includes an electron gun, a first condenser lens, a second condenser lens, an objective aperture, scan coils, and an objective lens arranged in this order in the direction of travel of the electron beam. The mode is switched by changing the excitation of the first and second condenser lenses and of the objective lens so that the electron beam is in focus at the specimen surface. The distance a between the principal plane of the objective lens and the focal point of the second condenser lens in the first mode and the distance b between the principal plane of the objective lens and the focal point of the second condenser lens in the second mode are set sufficiently larger than the maximum distance w.sub.2 between the principal plane of the objective lens and the specimen.

REFERENCES:
patent: 3889114 (1975-06-01), Van Oostrum
patent: 3937959 (1976-02-01), Namae
patent: 4199681 (1980-04-01), Namae
patent: 4429222 (1984-01-01), Yonezawa
patent: 4494000 (1985-01-01), Shii et al.
patent: 4880977 (1989-11-01), Tomita et al.
patent: 5013913 (1991-05-01), Benner
patent: 5032725 (1991-07-01), Kanda
patent: 5124556 (1992-06-01), Takashima

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