| 摘要 |
Method in which different focusing voltages are applied to respective electrodes which form said unipotential auxiliary lenses, the unipotential auxiliary lenses having differences in potential which decrease in the direction of advance of the beams. In one embodiment, of five electrodes which sequentially form two unipotential auxiliary lenses, the first, third and fifth electrodes receive, in common, a relatively high focusing voltage, the second electrode receives a relatively low focusing voltage, the fourth electrode receives an intermediate- level focusing voltage between the relatively high and relatively low voltages. According to this method, focusing at the auxiliary lens is attenuated and therefore variations in the electrical fields and the consequent variation of the characteristics of the beam points on account of electrode process errors are reduced. <IMAGE>
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