Method of operating a charged particle microscope and charged particle microscope operating according to such method

A charged particle microscope, comprising:

• a charged particle source generating a charged particle beam;
• at least one focusing lens traversed by the charged particle beam, the at least one focusing lens including an objective lens focusing the charged particle beam at a working distance from the objective lens;
• an x-stigmator traversed by the particle beam;
• an y-stigmator traversed by the particle beam;
• an object mount configured to hold the object at a distance from the objective lens;
• and
• a controller configured to provide settings of a focus, an x-stigmator and an y-stigmator of the charged particle microscope, and
• to repeatedly perform:
• adjusting the charged particle microscope to the settings,
• recording an image of an object using the settings,
• determining a sharpness measure of the image as a whole from the recorded image, the sharpness measure indicating an overall sharpness of the recorded image, and
• changing at least one of the settings based on the sharpness measure, until a stop criterion is fulfilled;
• wherein the determining of the sharpness measure comprises:
• determining an orientation of an intensity gradient at each of a plurality of locations within one of the recorded image and a processed image generated by processing the recorded image, and
• determining the sharpness measure based on the plurality of determined orientations;
• and
• wherein the adjusting of the charged particle microscope to the settings includes at least one of
• adjusting at least one of an excitation of the at least one focusing lens and a distance of the object mount from the objective lens according to the setting of the focus,
• adjusting an excitation of the x-stigmator according to the setting of the x-stigmator, and
• adjusting an excitation of the y-stigmator according to the setting of the y-stigmator.