Method and electron microscope for measuring the similarity of two-dimensional images

An electron microscope, comprising a digital image sensor, a device for tilting the electron beam relative to the object to be analyzed, a lens arrangement for correcting aberrations, and a controller for this lens arrangement, and an adjustment device for the lens arrangement, comprising:

• a simulation unit, which is able to deliver ideal electron-microscopic images of test structures having predetermined values for the defocusing and astigmatism thereof;
• a comparison unit, which is connected to the image sensor and the simulation unit and which is able to measure the similarity between an image supplied by the image sensor and by the simulation unit;
• and
• an evaluation unit, which is connected to the comparison unit and the controller and which is able to approximately determine the aberrations of the electron microscope from the measured similarity and the associated defocusing and astigmatism values and convert them into an adjustment command for the controller.

An electron microscope, comprising a digital image sensor, a device for tilting the electron beam relative to the object to be analyzed, a lens arrangement for correcting aberrations, a controller for this lens arrangement, and an adjustment device for the lens arrangement, comprising:

• a simulation unit, which is able to deliver ideal electron-microscopic images of test structures having predetermined values for the defocusing and astigmatism thereof;
• a comparison unit, which is connected to the image sensor and the simulation unit and which is able to measure the similarity between an image supplied by the image sensor and by the simulation unit;
• an evaluation unit, which is connected to the comparison unit and the controller and which is able to approximately determine the aberrations of the electron microscope from the measured similarity and the associated defocusing and astigmatism values and convert them into an adjustment command for the controller;
• said comparison unit partitioning the images into mutually identical subimages such that the extension of at least one subimage in the direction of the gradient of an additional signal is smaller than the extension of this subimage in the direction perpendicular thereto;
• mutually associated subimages being compared with one another;
• and
• the results of these comparisons being combined into an overall measure of the similarity of the two images.