Patent ID: 7714286

Claim:
A charged particle beam apparatus comprising: an electron optical system, which detects secondary particles generated by irradiation of a specimen with a primary charged particle beam and obtains secondary particle distribution data for an irradiation area of the charged particle beam in any focus state; and a processing unit which processes the secondary particle distribution data obtained by the electron optical system; wherein: the electron optical system comprises an aberration corrector which removes aberration of the primary charged particle beam on the specimen by giving reverse aberration to aberration generated by the electron optical system; and the processing unit: obtains derivative values in a plurality of directions for each item of secondary particle distribution data of the specimen, obtained in different focus states; obtains aberration parameters of the aberration based on asymmetry of distribution of the directional derivative values in the focus states; and determines operation conditions of the aberration corrector based on the obtained aberration parameters.