A method, device, charged particle-optical apparatus and an assessment apparatus

Abstract

The present invention provides a method of determining data representative of a focal surface of an array of charged particle beams and / or a height of a sample surface in a multi-beam charged particle-optical device, the method comprising: projecting beams onto a sample location at a first relative position; determining first individual focus values for individual beams; displacing the sample relative to the array of beams along a distance to a second relative position; determining second individual focus values for individual beams; displacing the sample relative to the array of beams along a distance to a third relative position; determining third individual focus values for individual beams in the array; and determining the data representative of the focal surface of the array of beams and / or the height of the sample surface based on the first individual focus values, the second individual focus values and the third individual focus values.

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