| 摘要 |
PROBLEM TO BE SOLVED: To improve the accuracy of the alignment of primary electron beam by interlocking modulation amplitude control of the exciting current of an objective lens for alignment with an image magnification, a focus current, and an accelerating voltage and expressing these parameters with a preset product. SOLUTION: When primary electrons are aligned with an objective lens, an observation magnification M when a focus position Z is constant, and an appropriate modulation amplitude of the objective lens in Z in a case of setting M to a fixed value are expressed by an exponential function with M as the base, F2 =M<b> and an exponential function with Z as the base, F1 =Z<a> respectively. The modulation amplitude of the appropriate objective lens in changing M and Z is expressed by the product of F1 by F2 and the focus characteristics of the objective lens is a value obtained by dividing a lens current Iobj by a square root√Vacc , of the accelerating voltage, and Z is calculated from Iobj /√Vacc . The modulation amplitude of the exciting current of the objective lens is controlled based on these relations so that highly precise alignment can be implemented.
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