Method and system for the removal and/or avoidance of contamination in charged particle beam systems

1. A charged particle beam system, comprising:

a beam generator module, comprising a charged particle beam generator for generating a beam of charged particles, said charged particle beam generator being arranged in said beam generator module;

a charged particle optical column arranged in a vacuum chamber, wherein said charged particle optical column is arranged for projecting said beam of charged particles onto a target, and wherein said charged particle optical column comprises a charged particle optical element for influencing said beam of charged particles;

a source for providing cleaning agent;

a conduit connected to said source and arranged for introducing said cleaning agent towards said charged particle optical element;

an aperture element comprising a plurality of apertures for letting through a plurality of charged particle beams from said beam of charged particles, the aperture element is arranged between said charged particle beam generator and said charged particle optical element; and

a restriction element provided between said charged particle beam generator and the aperture element for restricting a flow path between the beam generator module and the aperture element or a downstream module comprising the aperture element,

wherein the restriction element is movably connected to the beam generator module and arranged for abutting the aperture element or the downstream module comprising the aperture element.

2. The charged particle beam system according to claim 1 , wherein said restriction element is arranged for abutting the aperture element or the downstream module comprising the aperture element by means of gravity and/or a spring force.

3. The charged particle beam system according to claim 2 , wherein said restriction element is connected to a first wall of said beam generator module, said restriction element at least partly surrounding a perimeter of an opening in said first wall for passage of said beam of charged particles, wherein said restriction element comprises an at least partially ring-shaped element, said at least partially ring-shaped element being movably arranged with respect to said first wall in a direction toward or away from the aperture element.

4. The charged particle beam system according to claim 3 , wherein the at least partially ring-shaped element comprises a ceramic ring.

5. The charged particle beam system according to claim 3 , further comprising a confining element for confining a movement of said restriction element with respect to said first wall.

6. The charged particle beam system according to claim 5 , wherein said restriction element is provided with one or more protrusions and said confining element is arranged to cooperate with said protrusions to confine movement of said restriction element.

7. The charged particle beam system according to claim 1 , further comprising:

a modulation element arranged downstream the aperture element, said modulation element comprising a second plurality of apertures for passage of said charged particle beams and deflectors associated with said second plurality of apertures, said deflectors arranged to selectively deflect or not deflect said charged particle beams, and

a beam stop element comprising a third plurality of apertures for passage of charged particle beams and a blocking area for blocking charged particle beams, said beam stop element arranged downstream said modulation element,

said modulation element and said beam stop element arranged to function together to let pass or to block said selectively deflected charged particle beams, wherein said conduit is arranged to direct said cleaning agent toward said beam stop element.

8. The charged particle beam system according to claim 1 , wherein said charged particle optical element comprises:

a charged particle transmitting aperture for transmitting and/or influencing said beam of charged particles, and

a vent hole for providing a flow path between a first side and a second side of said charged particle optical element,

wherein the vent hole has a larger cross section than a cross section of the charged particle transmitting aperture.

9. The charged particle beam system according to claim 8 , wherein said vent hole has a cross section of one of the following shapes: circular, slit-shaped, or elliptical.

10. The charged particle beam system according to claim 8 , wherein the charged particle optical element comprises a plurality of said vent holes and a plurality of said charged particle transmitting apertures, said vent holes arranged next to said charged particle transmitting apertures.

11. The charged particle beam system according to claim 10 , wherein said charged particle transmitting apertures are arranged in one or more groups and the vent holes are arranged substantially along said one or more groups.

12. The charged particle beam system according to claim 11 , wherein said vent holes are arranged in one or more one dimensional arrays.

13. The charged particle beam system according to claim 11 , wherein said vent holes are arranged in one or more two-dimensional arrays.

14. The charged particle beam system according to claim 11 , wherein said vent holes are arranged on either sides of said one or more groups of plurality of charged particle transmitting apertures.

15. The charged particle beam system according to claim 10 , wherein said vent holes are arranged immediately adjacent an area comprising a plurality of said charged particle transmitting apertures.

16. The charged particle beam system according to claim 10 , wherein said vent holes are arranged with a pitch which is equal to or larger than a dimension of said vent holes, said pitch in particular being in the range from 1 to 3 times the dimension of said vent holes.

17. The charged particle beam system according to claim 16 , wherein said pitch is equal to or larger than a dimension of said vent holes along a direction of alignment of said vent holes.

18. The charged particle beam system according to claim 8 , wherein the system is configured such that a charged particle passing through said vent hole is prevented from reaching said target.

19. The charged particle beam system according to claim 8 , wherein said charged particle optical element comprises a beam stop element, said beam stop element comprising:

a plurality of charged particle transmitting apertures for passage of charged particle beams, and a non-aperture area for blocking passage of charged particles, and

a plurality of vent holes for providing a flow path through said beam stop element.

20. The charged particle beam system according to claim 8 , said system further comprising:

a projection lens comprising a plurality of projection lens apertures for focusing said charged particle beams, wherein said projection lens is arranged downstream said beam stop element, and wherein said projection lens and said beam stop element are arranged such that any charged particles passing through one or more of said vent holes are blocked by a non-aperture area of said projection lens.

21. The charged particle beam system according to claim 20 , wherein said vent holes have a cross section in a range from half of a cross section of said projection lens apertures to two times the cross section of said projection lens apertures.

22. The charged particle beam system according to claim 20 , wherein said projection lens further comprises a plurality of dummy apertures arranged around a group of said projection lens apertures, wherein said vent holes are arranged such that any charged particle passing through said vent holes are blocked by an area located laterally outside said dummy apertures.

23. The charged particle beam system according to claim 1 , wherein electrical connections within said charged particle optical system are provided with a protective coating including epoxy and/or a metal layer.

24. A method for preventing or removing contamination of a charged particle transmitting aperture in the charged particle beam system according to claim 1 , the method comprising the steps of:

providing the beam generator module above the aperture element or the downstream module comprising the aperture element; and

providing the restriction element between the beam generator module and the aperture element or the downstream module comprising the aperture element to restrict a flow path between the beam generator module and the aperture element or a downstream module comprising the aperture element,

wherein the restriction element is provided to be movably connected to the beam generator module and to abut the aperture element or the downstream module comprising the aperture element.

25. The method according to claim 24 , wherein the restriction element is provided to abut the aperture element or the downstream module comprising the aperture element by means of gravity and/or spring force.

26. The method according to claim 24 , further comprising the step of:

introducing a cleaning agent towards said charged particle optical element while said beam generator is generating said beam of charged particles and/or while a second charged particle beam source is generating a beam of charged particles which is directed toward said charged particle optical element.

27. The method according to claim 26 , wherein said charged particle optical element comprises a charged particle transmitting aperture for transmitting and/or influencing said beam of charged particles, and a vent hole for providing a flow path between a first side and a second side of said charged particle optical element, wherein the vent hole has a larger cross section than a cross section of the charged particle transmitting aperture,

wherein the method further comprising the step of:

maintaining a vacuum in said vacuum chamber while introducing said cleaning agent,

wherein the step of maintaining a vacuum comprises providing a flow at least through said charged particle optical element via a vent hole to a vacuum pump connected to said vacuum chamber.

28. The method according to claim 27 , comprising the step of preventing any charged particles passing through said vent hole from reaching said target.

29. The method according to claim 27 , wherein said charged particles passing through said vent hole are prevented from reaching said target by blocking these charged particles by non-aperture areas comprised in a further aperture element arranged downstream said charged particle optical element, said further aperture element comprising one or more apertures for passage of charged particle beams having passed through said charged particle transmitting apertures.

30. The method according to claim 26 , comprising introducing said cleaning agent in a region of said charged particle optical column where said charged particles have energy in the range of 1-10 k eV.

31. The method according to claim 26 , wherein one or more charged particle beams is present at or near the charged particle optical element while directing said cleaning agent toward the charged particle optical element.