Patent ID: 8129680

Claim:
A charged particle beam apparatus comprising: a charged particle optical system to scan a primary charged particle beam on a specimen, detect secondary charged particles emitted from the specimen due to the scanning and output the detection results as a secondary charged particle signal; a control unit for controlling the charged particle optical system; a data processing device to process the secondary charged particle signal that was output and acquire two-dimensional distribution information on pixels matching the area scanned by the primary charged particle beam, wherein the charged particle optical system includes: an aberration corrector to reduce the aberration generated by the charged particle optical system; and a unit to guide the charged particle beam from the optical axis of the charged particle beam in a tilted state onto the specimen, and wherein the data processing device: calculates an out-of-focus amount and astigmatic difference in the charged particle optical system from multiple two-dimensional distribution information acquired by scanning the specimen with the primary charged particle beam in a tilted state and also while changing a degree of focus and, calculates an optical order aberration coefficient to use in the charged particle optical system, by utilizing the two-dimensional distribution information obtained from scanning the specimen in a state where the primary charged particle beam is not tilted, and the calculated out-of-focus amount and astigmatic difference.