Patent ID: 8253112

Claim:
A focusing method for a charged particle beam comprising: setting a lens value in an imaging lens; setting first coil values in first and second alignment coils, wherein a charged particle beam is temporarily swung outside and then swung back to an opening center of a first aperture plate member by deflection of the first and second alignment coils in which the first coil values have been set; measuring a first position of the charged particle beam focused by the imaging lens in which the lens value has been set, on a second aperture plate member, wherein the charged particle beam having passed through the opening center of the first aperture plate member by deflection of the first and second alignment coils in which the first coil values have been set is focused on a position which is different from a position on the second aperture plate member, by the imaging lens in which the lens value has been set; setting second coil values in the first and second alignment coils, wherein the charged particle beam is temporarily swung outside and then swung back to the opening center of the first aperture plate member by deflection of the first and second alignment coils in which the second coil values have been set and an amount of deflection of the first and second alignment coils in which the second coil values have been set is different from an amount of deflection of the first and second alignment coils in which the first coil values have been set; measuring a second position of the charged particle beam focused by the imaging lens in which the lens value has been set, on the second aperture plate member, wherein the charged particle beam having passed through the opening center of the first aperture plate member by deflection of the first and second alignment coils in which the second coil values have been set is focused on a position which is different from a position on the second aperture plate member, by the imaging lens in which the lens value has been set; and calculating a difference between the first and second positions of the charged particle beam on the second aperture plate member; wherein the lens value is variably changed, and a plurality of the differences are calculated depending on the lens values variably changed; and further comprising: setting a lens value which corresponds to a minimum difference of the plurality of the differences, in the imaging lens.