Method of determining a beam convergence of a charged particle beam, and charged particle beam system

A method of determining a beam convergence of a charged particle beam focused by a focusing lens toward a sample in a charged particle beam system, comprising

• (a) taking one or more images of the sample when the sample is arranged at one or more defocus distances from a respective beam focus of the charged particle beam to provide one or more taken images;
• (b) simulating one or more images of the sample taken at the one or more defocus distances based at least on an estimated beam convergence value of the charged particle beam and on a focus image of the sample to provide one or more simulated images;
• (c) determining a magnitude (R) of a difference between the one or more taken images and the one or more simulated images;
• and
• (d) varying the estimated beam convergence value in an iterative process for reducing or minimizing said magnitude (R) to determine an actual beam convergence value.

A charged particle beam system, comprising:

• a charged particle source for emitting a charged particle beam propagating along an optical axis;
• a sample stage;
• a focusing lens for focusing the charged particle beam toward a sample placed on the sample stage;
• a charged particle detector for detecting signal particles emitted from the sample;
• and
• a processor and a memory storing instructions that, when executed by the processor, cause the charged particle beam system to:
• (x1) simulate one or more beam profiles at one or more defocus distances based at least on an estimated beam convergence value of the charged particle beam to provide one or more simulated beam profiles,
• (x2) compare one or more retrieved beam profiles retrieved from one or more images of the sample taken at the one or more defocus distances and the one or more simulated beam profiles for determining a magnitude of a difference therebetween;
• and
• (x3) vary the estimated beam convergence value in an iterative process for reducing or minimizing said magnitude to determine an actual beam convergence value.