Scanning electron microscope

A scanning electron microscope having an electron optics column for irradiating an electron beam on a specimen, a specimen stage for holding a specimen to be observed and a specimen chamber for housing the specimen stage, whereby charged particles given off from the specimen under irradiation of the electron beam are gas-amplified through their interaction with gas molecules prevailing in the specimen chamber and amplified ions are detected as positive induced current, comprising:

• a first detection electrode for detecting an induced current attributable to backscattering electrons out of charged particles given off from said specimen to be observed under irradiation of the electron beam;
• a second detection electrode for detecting an induced current attributable to secondary electrons out of charged particles given off from said observed specimen under the electron beam irradiation;
• and
• means for separating ions attributable to gas amplification by the backscattering electrons and ions attributable to gas amplification by the secondary electrons and transferring them to said first and second detection electrodes, respectively,
• wherein:
• said means for transferring the gas-amplified ions includes an electric field supply electrode for gas amplification interposed between said specimen stage and said first detection electrode,
• said first detection electrode is arranged at a position constantly distant from the optical axis of the illuminating electron beam in a space defined by the bottom of said electron optics column and said specimen stage, having its bombardment surface confronting said specimen stage,
• said first detection electrode is constructed of a disk-shaped electrode, said second electrode is constructed of a cylindrical electrode arranged symmetrically with the center axis of said bombardment surface, and
• said electric field supply electrode is arranged internally of said cylinder.