A method for correcting drifts in beam irradiation position in a focused ion
beam
apparatus is disclosed. A linear line pattern is formed on a sample by linearly
irradiating a focused ion beam at a location removed from a processing region where
a cross section is to be formed in the sample. The linear line pattern extends
in a direction in parallel with a surface of the cross section to be formed. By
referring to the linear line pattern while a specified section of the sample is
processed, the beam irradiation position of the focused ion beam with respect to
the linear line pattern is measured in a direction perpendicular to the linear
line pattern to detect a drift in the beam irradiation position of the focused
ion beam in the direction perpendicular to the linear line pattern. The beam irradiation
position of the focused ion beam is corrected based on the drift detected with
respect to the processing region.
