Focused ion beam system

A focused ion beam system comprising:

• a liquid metal ion source;
• a condenser lens which processes an ion beam generated by the liquid metal ion source;
• and
• an objective lens which focuses the ion beam which has passed through the condenser lens and emits the ion beam onto a surface of a sample, wherein
• the condenser lens works to process the ion beam into a collimated form,
• an electrical aperture unit is disposed between the condenser lens and the objective lens, the electrical aperture unit working to alter an area through which the ion beam, as processed by the condenser lens, passes to control a diameter of the ion beam,
• the electrical aperture unit includes a plurality of beam shielding plate units, each of the beam shielding plate units being equipped with a p pair of beam shielding plates which are diametrically opposed to each other across the ion beam which has passed through the condenser lens and movable in a direction perpendicular to an optical axis of the ion beam,
• the beam shielding plates of the beam shielding plate units are arranged around the ion beam to define the area through which the ion beam passes,
• the plurality of beam shielding plate units are offset from each other in a direction in which the optical axis of the ion beam extends, and
• an astigmatism alignment device is disposed downstream of the electrical aperture unit, the astigmatism alignment device including a plurality of pole lenses arranged around the ion beam, and wherein the electrical aperture unit includes the beam shielding plates which are identical in number with the pole lenses.