received by the International Bureau on 8 May 2018 (08.05.18)

+ STATEMENT

1. Method for preventing or removing contamination of a charged particle transmitting aperture in a charged particle beam system arranged in a vacuum chamber, the charged particle beam system comprising a charged particle optical column for projecting a beam of charged particles onto a target, said charged particle optical column comprising a charged particle optical element for influencing the beam of charged particles,

said charged particle optical element comprises said charged particle transmitting aperture for transmitting and/or influencing said beam of charged particles, and a vent hole providing a flow path from a first side to a second side of said charged particle optical element;

the method comprising the following steps:

- introducing a cleaning agent towards said charged particle optical element while a beam of charged particles is present at or near said charged particle optical element;

- maintaining a vacuum in said vacuum chamber, wherein the step of maintaining a vacuum comprises enabling a flow or movement of species at lea3t through said charged particle optical element via said vent hole to a vacuum pump connected to said vacuum chamber; and

preventing any charged particles passing through said at least one vent hole from reaching said target, or preventing charged particles from reaching the vent hole.

2. Method according to claim 1, wherein said charged particle optical element is stopping or at least partly blocking said beam of charged particles and/or wherein said charged particle transmitting aperture is acting as a current limiting aperture.

3. Charged particle beam system (201, 301), comprising:

- a charged particle beam generator (16, 216) for generating a beam of charged particles (20);

- a charged particle optical column (206, 306) arranged in a vacuum chamber, wherein said charged particle optical column is arranged for projecting said beam of charged particles onto a target (12), and wherein said charged particle optical column comprises a charged particle optical element (226) for influencing said beam of charged particles;

- a source (62) for providing cleaning agent (100);

- a conduit (64) connected to said source and arranged for introducing said cleaning agent towards said charged particle optical element;

wherein said charged particle optical element comprises:

- a charged particle transmitting aperture (46) for transmitting and/or influencing said beam of charged particles, and

- a vent hole (60, 60a, 60b) for providing a flow path (Γ3) between a first side and a second aide 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 one or more elements or components are arranged downstream of the charged particle optical element to block a further path of any charged particles transmitted through the vent hole, or an element or component is provided upstream the vent hole, for preventing charged particles from reaching the vent hole.

4. System according to claim 3, wherein said charged particle optical element is arranged for stopping or at least partly blocking said beam of charged particles and/or said charged particle transmitting aperture acting as a current limiting aperture.

5. System according to claim 3 or 4, 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.

6. System according to any one of claims 3-5, wherein said vent holes are arranged with a pitch (p) 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.

7. System according to any one of claims 3-6, wherein said charged particle optical element comprises a beam stop element (226) , said beam stop element comprising:

a plurality of said charged particle transmitting apertures (46) for passage of charged particle beams, and a non-aperture area for blocking passage of charged particles, and

- a plurality of vent holes (60, 60a_r 60b for providing a flow path (F3) through said beam stop element.

8. System according to claim 7, said system further comprising

- a projection lens (29) comprising a plurality of projection lens apertures (58) for focusing said charged particle beams (8), 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.

9. System according to claim 8, 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.

10. System according to claim 8 or 9, wherein said projection lens further comprises a plurality of dummy apertures (70) 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.

11. System according to any one of claims 3-10, further comprising

- a second aperture element (23) comprising a plurality of apertures (66) for forming a plurality of charged particle beams (B) from said beam (20) of charged particles, said second aperture element arranged between said charged particle beam generator and said charged particle optical element, and

- a restriction element (76) provided between said charged particle beam generator and said second aperture element, said restriction element arranged for preventing or at least reducing a flow of said cleaning agent and/or products thereof to said charged particle beam generator.

12. System according to claim 11, further comprising:

- a beam generator module, said charged particle beam generator being arranged in said beam generator module; a modulation module (225) , said second aperture element being arranged in said modulation module; wherein said restriction element is movably connected to said beam generator module and arranged for abutting said modulation module by means of gravity and/or a spring force.

13. System according to claim 12, wherein said restriction element (76) is connected to a first wall (82) of said beam generator module, said restriction element at least partly surrounding a perimeter of an opening (80) In said first wall for passage of said beam of charged particles, wherein said restriction element comprises an at least partially ring-shaped element (76), in particular a ceramic ring, said at least partially ring-shaped element being movably arranged with respect to said first wall in a direction toward or away from said modulation module . 14. System according to claim 13, further comprising a confining element (78) for confining a movement of said restriction element with respect to said first wall, wherein said restriction element is provided with one or more protrusions (77) and said confining element (78) is arranged to cooperate with said protrusions to confine movement of said restriction element.

15. System according to any one of claims 11-14, further comprising:

- a modulation element (24) arranged downstream said second aperture element (23) , said modulation element comprising a second plurality of apertures (46) 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

said charged particle optical element comprising a beam stop element (226) comprising a third plurality of apertures (46) for passage of charged particle beams (8) 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 (64) is arranged to direct said cleaning agent toward said beam stop element -

16. Method for preventing or removing contamination of a charged particle transmitting aperture in the charged particle beam system according to any one of the preceding claims 3-15, the method comprising the steps of:

- introducing a cleaning agent towards said charged particle optical element while said beam generator (16, 216) 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; and

- maintaining a vacuum in said vacuum chamber

(2) while introducing said cleaning agent,

wherein the step of maintaining a vacuum comprises providing a flow or movement of species at least through said charged particle optical element via said vent hole (60, 60a, 60b) to a vacuum pump connected to said vacuum chamber

further comprising the step of preventing any charged particles passing through said at least one vent hole from reaching said target, and/or blocking charged particles upstream of the at least one vent hole.

17. Method according to claim 16, wherein said charged particles passing through said vent hole are prevented from reaching said target (12) 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 aperture.

18. Method according to any one of claims 16-17, further comprising the following steps:

- arranging said charged particle beam generator in a beam generator module and said charged particle optical element in a modulation module,

providing a restriction element, movably connected to said beam generator module and abutting said modulation module by means of gravity and/or spring force. 19. Method according to any one of claims 16 to

18, comprising introducing said cleaning agent in a region of said charged particle optical column where said charged particles have an energy in the range of 1-lOkEV, in particular around or lower than 5keV.

20. Method according to any one of claims 16 to

19, 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.

21. A charged particle beam system, comprising: a charged particle beam generator for generating a beam of charged particles;

- a charged particle optical column arranged in a vacuum chamber, wherein the charged particle optical column is arranged for projecting the beam of charged particles onto a target, and wherein the charged particle optical column comprises a charged particle optical element comprising a plurality of charged particle transmitting apertures;

- a source for providing a cleaning agent;

a conduit connected to the source for introducing the cleaning agent towards the charged particle optical element;

a second aperture element, comprising a plurality of apertures for forming a plurality of charged particle beams from the beam of charged particles, the second aperture element arranged between the charged particle beam generator and the charged particle optical element, and

- a restriction element provided between the charged particle beam generator and the second aperture element, the restriction element preventing or at least minimizing a flow or passage of said cleaning agent and/or products thereof to the charged particle beam generator.

22. System according to claim 21, further comprising:

- a beam generator module (216), said charged particle beam generator being · arranged in said beam generator module;

a modulation module (225), said second aperture element being arranged in said modulation module;

wherein said restriction element is movably connected to said beam generator module and arranged for abutting said modulation module by means of gravity and/or a spring force.

23. System according to claim 22, wherein said restriction element (76) is connected to a first wall (82) of said beam generator module, said restriction element at least partly surrounding a perimeter of an opening (80) in said first wall for passage of said beam of charged particles, wherein said restriction element comprises an at least partially ring-shaped element (76), said at least partially ring-shaped element being movably arranged with respect to said first wall in a direction toward or away from said modulation module.