Electron microscope and specimen tilt angle adjustment method

An electron microscope comprising:

• an irradiation lens system that irradiates a specimen with an electron beam;
• an irradiation system deflector that deflects an electron beam incident on the specimen;
• a specimen tilting mechanism that tilts the specimen;
• an imaging lens system that forms an electron diffraction pattern or an electron microscope image by using an electron having passed through the specimen;
• an imaging device that acquires the electron diffraction pattern or the electron microscope image formed by the imaging lens system;
• and
• a controller that controls the irradiation system deflector and the specimen tilting mechanism,
• the controller configured to:
• acquire a plurality of electron diffraction patterns formed by using electron beams having different incidence angles to the specimen, the different incidence angles having been obtained by deflecting the electron beams incident on the specimen by using the irradiation system deflector;
• calculate a tilt angle of the specimen based on the plurality of electron diffraction patterns;
• and
• control the specimen tilting mechanism so that the specimen has the calculated tilt angle, wherein
• the specimen tilting mechanism has two tilting axes,
• the irradiation system deflector has two tilting axes,
• the two tilting axes of the specimen tilting mechanism and the two tilting axes of the irradiation system deflector do not coincide with each other, and
• when the controller acquires the plurality of electron diffraction patterns, the plurality of electron diffraction patterns are acquired by:
• deflecting an electron beam by using the irradiation system deflector so that the same electron diffraction pattern as that when the specimen was tilted about one of the tilting axes of the specimen tilting mechanism is obtained;
• and
• deflecting an electron beam by using the irradiation system deflector so that the same electron diffraction pattern as that when the specimen was tilted about the other tilting axis of the specimen tilting mechanism is obtained.

A specimen tilt angle adjustment method in an electron microscope including an irradiation lens system that irradiates a specimen with an electron beam, an irradiation system deflector that deflects an electron beam incident on the specimen, a specimen tilting mechanism that tilts the specimen, an imaging lens system that forms an electron diffraction pattern or an electron microscope image by using an electron having passed through the specimen, and an imaging device that acquires the electron diffraction pattern or the electron microscope image formed by the imaging lens system,

• the method comprising:
• acquiring a plurality of electron diffraction patterns formed by using electron beams having different incidence angles BT1 and BT2 to the specimen, the different incidence angles BT1 and BT2 having been obtained by deflecting the electron beams incident on the specimen by using the irradiation system deflector;
• calculating a tilt angle of the specimen based on the plurality of electron diffraction patterns;
• and
• tilting the specimen to have the calculated tilt angle, wherein:
• the calculated tilt angle comprises the combination of tilt angles of the specimen in a first direction STx and a second direction STy that is perpendicular to STx;
• STx=BT1 cos θ+BT1 sin θ;
• STy=BT2 cos θ+BT2 sin θ;
• and
• θ=an angle between a tilting axis of the specimen tilting mechanism and a tilting axis of the irradiation system deflector
• wherein:
• the controller calculates the tilt angle by;
• calculating an electron diffraction spot coordinate for each of the plurality of acquired electron diffraction patterns, and performing circular approximation on each of the electron diffraction patterns based on the electron diffraction spot coordinate to calculate a radius of an approximate circle;
• calculating the incidence angle at which the calculated radius of the approximate circle is minimized by fitting;
• and
• calculating the tilt angle from the calculated incidence angle;
• and wherein:
• the specimen tilting mechanism has two tilting axes;
• the irradiation system deflector has two tilting axes;
• and
• the two tilting axes of the specimen tilting mechanism and the two tilting axes of the irradiation system deflector do not coincide with each other.