Charged particle beam adjustment method, charged particle beam drawing method, and charged particle beam irradiation apparatus

A charged particle beam irradiation apparatus comprising:

• an emitter configured to emit a charged particle beam with a predetermined emission current;
• an electron lens provided on a downstream side of the emitter and configured to adjust a focus of the charged particle beam with a lens value;
• an aperture substrate disposed on the downstream side of the electron lens and including a hole disposed to be a focus position of the charged particle beam;
• a calculator configured to calculate a first function of a first resolution obtained by scanning the aperture substrate using a plurality of the lens values with the charged particle beam emitted at a first adjustment value, which is the emission current smaller than a target value used for drawing, and the plurality of lens values, calculate, from the first function, a lens value range obtained by adding a predetermined margin to a lens value at a just focus where resolution is minimized during actual drawing of the charged particle beam in the electron lens, calculate a second function of second resolution obtained by scanning, with a charged particle beam emitted at a second adjustment value, which is the emission current larger than the first adjustment value and equal to or smaller than the target value, the aperture substrate using the plurality of lens values avoiding the lens value range and the plurality of lens values, and estimate a lens value at the just focus from the second function;
• and
• an adjuster configured to adjust the electron lens to the estimated lens value at the just focus.