US Patent 10020162 Beam alignment method and electron microscope

There is provided a beam alignment method capable of easily aligning an electron beam with a coma-free axis in an electron microscope. The method starts with tilting the electron beam (EB) in a first direction (+X) relative to a reference axis (A) and obtaining a first TEM (transmission electron microscope) image. Then, the beam is tilted in a second direction (−X) relative to the reference axis, the second direction (−X) being on the opposite side of the reference axis (A) from the first direction (+X), and a second TEM image is obtained. The reference axis is incrementally varied so as to reduce the brightness of the differential image between a power spectrum of the first TEM image and a power spectrum of the second TEM image.