| 摘要 |
PURPOSE:To make it possible to control the amount of current of electron beams radiated on a sample without deteriorating a focusing characteristic of the electron beams by disposing an electric field radiation emitter, a drawing electrode, an acceleration electrode, first and second electrostatic focusing lenses. CONSTITUTION:Two-staged electrostatic focusing lenses 20 and 21 are interposed between a drawing electrode 16 and an acceleration electrode 18. Intensities of the lenses 20 and 21 are changed in accordance with acceleration voltage and the desired amount of current of the electron beams so that a crossover image formed by the lenses 20 and 21 is always uniformly positioned. Hence, an object lens 27 is not required to be regulated even in changes of the acceleration voltage and the amount of current. Therefore, no image rotates by the object lens 27 and so a scanning direction of the electron beams can be maintained constantly. Resultingly, even if the acceleration voltage and the amount of current of electron beams are changed depending on the sample 28, the scanning direction of the electron beams does not change regarding a pattern to be measured so that high precision measurement can be performed. Besides, a focusing characteristic of the electron beams can be improved by interposing the lenses 20, 21 between the emitter 11 and the acceleration electrode 18. !.
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