Alignment determination method and computer program

A non-transitory computer readable medium that stores a set of instructions for determining alignment of electron optical components operable on a plurality of beamlets in a charged particle apparatus comprising:

• an aperture array and a detector configured to detect charged particles corresponding to the beamlets that pass through the corresponding apertures in the aperture array, the detector positioned downbeam along the paths of the beamlets relative to the aperture array, the set of instructions configured to cause one or more processors of the charged particle apparatus to perform operations comprising:
• control the charged particle apparatus to scan each beamlet in a plane of the aperture array over a portion of the aperture array in which a corresponding aperture of the aperture array is defined so that charged particles of each beamlet may pass through the corresponding aperture;
• control the charged particle apparatus to detect during the scan any charged particles corresponding to each beamlet that passes through the corresponding aperture;
• generate a detection pixel for each beamlet based on the detection of charged particles corresponding to each beamlet at intervals of the scan;
• collect information comprised in the detection pixel such as the intensity of charged particles;
• generating, for each beamlet, an image representative of the intensity of detected signal particles corresponding to the scan of the beamlet over the portion of the aperture array in which its corresponding aperture is defined;
• and
• determining a parameter set of at least one beamlet relating to dimensions of the at least one beamlet in a plane of the aperture array, based on the image corresponding to the at least one beamlet.