| 摘要 |
PURPOSE:To enable the automatic setting of the optimum accelerating voltage and so forth, by detecting the time variation of secondary electron signal at the time of the irradiation of an electron beam on a specimen and choosing the accelerating voltage giving the least variation. CONSTITUTION:A specimen 8 is irradiated with an electron beam 7 generated by a certain accelerating voltage and a switching circuit 12 is operated, the specimen signal VS1 at the time of T1 being measured which is taken into a memory 14 after the A/D conversion by a converter 13. Next, the specimen signal VS2 at the time of T2 taken into is compared with the signal VS1 and computed by a computer 19. In case of VS1/VS2<1, a signal 20 changing the accelerating voltage according to an instruction of the computer 19 is transmitted to a high voltage circuit 15. Thereby, the accelerating voltage is changed and the optimum voltage suitable for the condition of VS1/VS2approx.=1 is chosen by the computer 19. Thus, observation, analysis and measurement can be performed without relying upon an operator's experience and perception.
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