Multi charged particle beam irradiation apparatus and adjusting method thereof

A multi charged particle beam irradiation apparatus comprising:

• a charged particle source configured to generate and emit multiple beams;
• an optical system including a plurality of lenses configured to adjust the multiple beams emitted from the charged particle source;
• and
• a lens control circuit configured to control the plurality of lenses,
• wherein the optical system is configured such that a virtual crossover as viewed from a downstream side of the multiple beams is formed in an anterior focal plane of an objective lens being a lowermost lens of the plurality of lenses, the anterior focal plane being located opposite a sample surface with respect to the objective lens, and that the multiple beams passed through the objective lens are perpendicularly incident on the sample surface;
• the plurality of lenses include three or more focus correcting lenses configured to perform focus correction of the multiple beams in accordance with a height of the sample surface and/or beam current;
• an actual crossover (CO2r) is located between a principal surface of an uppermost focus correcting lens of the three or more focus correcting lenses and a principal surface of a lowermost focus correcting lens of the three or more focus correcting lenses;
• and
• the lens control circuit is configured to control a voltage applied to or a current passed through each of the focus correcting lenses such that a predetermined rotation angle condition, a condition under which a virtual crossover (CO2) as viewed from the downstream side is unchanged, and an in-focus condition are satisfied.