Multiple charged-particle beam apparatus with low crosstalk

1. A multi charged-particle beam apparatus comprising:

an electro-optical system for projecting a plurality of secondary charged-particle beams from a sample onto a charged-particle detector, the electro-optical system comprising a beam-limit aperture plate having a surface that is substantially perpendicular to an optical axis, the beam-limit aperture plate comprising:

a first aperture at a first distance relative to the surface of the beam-limit aperture plate; and

a second aperture at a second distance relative to the surface of the beam-limit aperture plate, wherein the second distance is different from the first distance,

wherein the charged-particle detector includes a plurality of detection elements, a respective detection element of the plurality of detection elements being associated with a corresponding beam of a plurality of secondary charged-particle beams.

2. The multi charged-particle beam apparatus of claim 1 , wherein the first aperture is a part of a first set of apertures of the beam-limit aperture plate at the first distance.

3. The multi charged-particle beam apparatus of claim 2 , wherein the second aperture is a part of a second set of apertures of the beam-limit aperture plate at the second distance.

4. The multi charged-particle beam apparatus of claim 3 , wherein a distance between the first distance and the second distance is 10 mm or less.

5. The multi charged-particle beam apparatus of claim 3 , wherein at least one set of the first and second sets of apertures comprises a plurality of apertures of different sizes.

6. The multi charged-particle beam apparatus of claim 3 , wherein the plurality of apertures of at least one set of the first and second sets are arranged in a linear, a rectangular, a circular, or a spiral pattern.

7. The multi charged-particle beam apparatus of claim 1 , wherein the optical axis is a secondary optical axis of the electro-optical system.

8. The multi charged-particle beam apparatus of claim 1 , wherein the first aperture is placed away from the second aperture along a second axis perpendicular to the optical axis.

9. The multi charged-particle beam apparatus of claim 1 , wherein the plurality of secondary charged-particle beams overlap to create a crossover area on a crossover plane perpendicular to the optical axis of the electro-optical system.

10. The multi charged-particle beam apparatus of claim 9 , wherein the first aperture and the second aperture of the beam-limit aperture plate are located on or within a range of positions of a crossover plane perpendicular to the optical axis.

11. The multi charged-particle beam apparatus of claim 10 , wherein the range of positions of the crossover plane is determined based on a landing energy of the plurality of primary charged-particle beams on the sample or an excitation of objective lens.

12. The multi charged-particle beam apparatus of claim 9 , wherein the beam-limit aperture plate is configured to move along a second axis perpendicular to the optical axis to position the first aperture at a first position and the second aperture at a second position, wherein the first aperture is aligned with the plurality of secondary charged-particle beams that overlap to form a first crossover plane at the first distance, wherein the second aperture is aligned with the plurality of secondary charged-particle beams that overlap to form a second crossover plane at the second distance, and wherein the first and second crossover planes are substantially perpendicular to the optical axis.

13. The multi charged-particle beam apparatus of claim 1 , wherein the beam-limit aperture plate is not movable along the optical axis.

14. The multi charged-particle beam apparatus of claim 1 , wherein the first aperture and the second aperture have different sizes.

15. The multi charged-particle beam apparatus of claim 1 , further comprising a charged-particle detector including a plurality of detection elements, wherein a respective detection element of the plurality of detection elements is associated with a corresponding beam of a plurality of secondary charged-particle beams.

16. The multi charged-particle beam apparatus of claim 1 , wherein the plurality of secondary charged-particle beams comprises at least one of secondary electrons or back-scattered electrons generated from the sample in response to an interaction between a plurality of primary charged-particle beams and the sample.

17. The multi charged-particle beam apparatus of claim 1 , wherein the first aperture and the second aperture have different sizes.

18. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of an electro-optical system to cause the electro-optical system to perform a method of controlling a beam-limit aperture plate of the electro-optical system to form images of a sample, the method comprising:

determining a position of a crossover plane associated with a plurality of secondary charged-particle beams generated from the sample;

determining a location for moving the beam-limit aperture plate to position one of a plurality of apertures of the beam-limit aperture plate in the crossover plane to cause the one of the plurality of apertures to align with the plurality of secondary charged-particle beams, wherein the beam-limit aperture plate has a surface positioned substantially perpendicular to an optical axis, the beam-limit aperture plate comprising:

a first aperture and a second aperture of the plurality of apertures, the first aperture at a first distance relative to the surface of the beam-limit aperture plate, and the second aperture at a second distance relative to the surface of the beam-limit aperture plate, the second distance being different from the first distance; and

moving, according to the determined location, the beam-limit aperture plate along a second axis substantially perpendicular to the optical axis to position the one of the plurality of apertures to be aligned with the plurality of secondary charged-particle beams that overlap to form the crossover plane.

19. The non-transitory computer readable medium of claim 18 , wherein the set of instructions that is executable by the at least one processor of an electro-optical system to cause the electro-optical system to further perform:

determining a change of the position of the crossover plane based on a change of a landing energy of the plurality of primary charged-particle beams on the sample or an excitation of object lens; and

moving the beam-limit aperture plate along the second axis to position the first aperture at a first position and the second aperture at a second position, wherein the first aperture is aligned with the plurality of secondary charged-particle beams that overlap to form a first crossover plane at the first distance, wherein the second aperture is aligned with the plurality of secondary charged-particle beams that overlap to form a second crossover plane at the second distance, and wherein the first and second crossover planes are substantially perpendicular to the optical axis.

20. A method of controlling a beam-limit aperture plate of a secondary imaging system to form images of a sample, the method comprising:

determining a position of a crossover plane associated with a plurality of secondary charged-particle beams generated from the sample;

determining a location for moving the beam-limit aperture plate to position one of a plurality of apertures of the beam-limit aperture plate in the crossover plane to cause the one of the plurality of apertures to align with the plurality of secondary charged-particle beams, wherein the beam-limit aperture plate has a surface positioned substantially perpendicular to an optical axis, the beam-limit aperture plate comprising:

a first aperture of the plurality of apertures, wherein the first aperture is at a first distance relative to the surface of the beam-limit aperture plate, and

a second aperture of the plurality of apertures, wherein the second aperture is at a second distance relative to the surface of the beam-limit aperture plate, the second distance being different from the first distance; and

moving, according to the determined location, the beam-limit aperture plate along a second axis substantially perpendicular to the optical axis to position the one of the plurality of apertures to be aligned with the plurality of secondary charged-particle beams that overlap to form the crossover plane.