Scanning electron microscope
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United States of America Patent
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-
Feb 5, 1991
Grant Date -
N/A
app pub date -
Sep 28, 1989
filing date -
Sep 30, 1988
priority date (Note) -
Expired
status (Latency Note)
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Abstract
In a field emission gun, current intensity of the electron beam passing through the gun anode contains a fluctuation component due to the ion bombardment and ion absorption near the emitter tip. For this reason, a scanning electron microscope having a field emission gun usually incorporates a fluctuation compensation device, which generates the signal ratio of the secondary electron signal from a specimen irradiated by the electron beam and the monitor signal corresponding to the current intensity of the electron beam passing through the gun anode and supplies the signal ratio for brightness modulation signal to the scanning image display means of the microscope. However, if the electron beam intensity is varied in a very wide operating range, the conventional fluctuation compensation device cannot operate with enough compensation effect. In this invention, the signal level of the monitor signal is maintained constant, so that the fluctuation correction device operates with enough compensation effect for a wide operating range of electron beam intensity.
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