Low-vacuum scanning electron microscope

#1. Field of the Invention

#The present invention relates to a low-vacuum scanning electron microscope that can maintain the interior of a specimen chamber at a low vacuum, can prevent charging of a specimen, and permits observation of a specimen in its intact state even if it contains moisture.

#2. Description of Related Art

#FIG. 1 is a schematic diagram of one conventional scanning electron microscope;

#FIG. 2 is a schematic diagram of another conventional scanning electron microscope;

#FIG. 3 is a schematic diagram of a scanning electron microscope according to the present invention;

#Preferred embodiments of the present invention are hereinafter described with reference to the accompanying drawings. FIG. 3 shows one example of a low-vacuum scanning electron microscope according to the present invention. This microscope has a microscope column 20. An electron gun chamber 21 is disposed in an upper part of the column 20. An electron gun, such as a thermionic gun or field emission gun, is mounted within the electron gun chamber 21.

#A primary electron beam 2 generated and accelerated by the electron gun is sharply focused onto a specimen 25 by a system of condenser lenses composed of condenser lenses 22 and an objective lens 23, the specimen 25 being positioned within a specimen chamber 24. Scan coils 26 for deflecting the primary electron beam 2 are mounted over the objective lens 23. Scanning signals are supplied to the scan coils 26 from a scanning signal generator circuit (not shown) to raster-scan a desired area on the specimen 25 with the primary electron beam.

#An aperture plate 27 having a minute opening is mounted at the bottom of the objective lens 23. The space extending from the electron gun chamber 21 to the inside of the objective lens 23 is partitioned from the inside of the specimen chamber 24 by the aperture plate 27. Therefore, the electron gun chamber 21 and the space over the objective lens 23 are evacuated to a high vacuum by a diffusion pump or the like via an exhaust pipe 28, while the inside of the specimen chamber 24 can be maintained at a low vacuum.