Tool for testing an electron-optical assembly

A method of testing an electron-optical assembly, the method comprising:

• while an electron-optical device comprising the electron-optical assembly, is not installed in a charged particle apparatus for SEM or lithography, illuminating the electron-optical assembly with at least one beam of charged particles such that charged particles in the at least one beam are transmitted through the electron-optical assembly in a plurality of sub-beams;
• detecting sub-beams of charged particles that have been transmitted through the electron-optical assembly;
• and
• determining the performance of the electron-optical assembly in dependence on the detected sub-beams;
• wherein the test of the determination of the performance of the electron-optical assembly is made prior to use of the electron-optical device that comprises the electron-optical assembly, in the charged particle apparatus for SEM or lithography.

An electron-optical assembly testing system for testing an electron-optical assembly prior to use of an electron-optical device comprising the electron-optical assembly, in a charged particle apparatus for SEM or lithography, the electron-optical assembly testing system comprising:

• a source of charged particles configured to emit a beam of charged particles;
• an electron-optical assembly holder configured to hold an electron-optical assembly for testing the electron optical assembly by transmission of charged particle beams from the source through the electron optical assembly, the electron-optical assembly for use in an electron-optical device in a charged particle apparatus for SEM or lithography, wherein the source of charged particles is configured to emit the beam of charged particles at a lower power than a charged particle source in the charged particle apparatus for SEM or lithography;
• and
• a sub-beam detector configured to detect sub-beams of charged particles transmitted from the source through the electron-optical assembly held by the holder while the electron-optical device comprising the electron-optical assembly is not installed in the charged particle apparatus for SEM or lithography.