System and method for alignment of secondary beams in multi-beam inspection apparatus

A method of inspecting a wafer using a multi-beam system with a secondary projection system to project a plurality of secondary electron beams onto a detection surface, the method comprising:

• determining a location of a desired bending point of an adjustable beam separator based on alignment characteristics of the secondary projection system;
• and
• adjusting one or more control signals to the adjustable beam separator to cause an effective bending point of the adjustable beam separator to be moved along a primary optical axis toward the location of the desired bending point;
• wherein the adjustable beam separator comprises a first Wien filter and a second Wien filter, and the one or more control signals comprise a first excitation input to the first Wien filter and a second excitation input to the second Wien filter to individually control each of the first and the second Wien filters.

A non-transitory computer readable medium storing a set of instructions that are executable by one or more processors of a multi-beam apparatus having a primary projection system and a secondary projection system to cause the multi-beam apparatus to perform operations for projecting a plurality of secondary electron beams onto a detection surface, the operations comprising:

• determining a location of a desired bending point of an adjustable beam separator in the primary projection system based on alignment characteristics of the secondary projection system;
• and
• adjusting one or more control signals to the adjustable beam separator to cause an effective bending point of the adjustable beam separator to be moved along a primary optical axis toward the location of the desired bending point;
• wherein the adjustable beam separator comprises a first Wien filter and a second Wien filter, and the one or more control signals comprise a first excitation input to the first Wien filter and a second excitation input to the second Wien filter to individually control each of the first and the second Wien filters.