| 摘要 |
A scanning electron microscope capable of producing a stable image even if an automated focusing operation is being performed. The microscope has a secondary electron detector, a vertical scanning signal generator, and an image memory connected with a CRT. The output signal from the detector is supplied to the image memory via an amplifier and an A/D converter and also to an integrator via a filter circuit and an absolute value circuit. The specimen is scanned to produce an image and is substantially simultaneously scanned to gather data for adjusting the focus by stepwise adjusting the objective lens current. The stepwise adjustment of the objective lens takes place only during scanning to gather data.
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