received by the International Bureau on 29 June 2015 (29.06.2015)

1. Cathode arrangement (20) comprising:

- a cathode body (22) housing an emission surface (32) for emitting electrons in a longitudinal direction (Z), wherein the emission surface is bounded by an emission perimeter (35);

- a focusing electrode (40) at least partially enclosing the cathode body in a transversal direction (X, Y) and comprising an electron transmission aperture (44) for focusing the electrons emitted by the emission surface, wherein the aperture is bounded by an aperture perimeter (45),

wherein the cathode body is moveably arranged within the focusing electrode allowing it to be displaced from an aligned position (R0) over a maximum transversal distance (dl),

and wherein the aperture perimeter transversally extends over the emission surface and beyond the emission perimeter over an overlap distance (d2) that exceeds the maximum transversal distance (dl).

2. Arrangement according to claim 1, wherein the focusing electrode comprises a cylindrical shell (54) having an inner surface facing an outer surface of the cathode body and provided with radial spacers or tabs (59) for providing an annular gap between the inner surface of the cylindrical shell and the cathode body

3. Arrangement (20) according to claim 1 , wherein the overlap distance (d2) is in a range of 10 micrometers to 100 micrometers, preferably equal to 50 micrometers.

4. Arrangement (20) according to any one of the preceding claims, wherein the

aperture perimeter (45) and the emission perimeter (35) are similarly shaped, and preferably are circular. Arrangement (20) according to any one of the preceding claims, wherein the focusing electrode (40) has an inner electrode surface (46) facing the emission surface (32), and wherein three spacing elements (48) are arranged for providing a spacing between the focusing electrode and the emission portion.

Arrangement (20) according to claim 5, wherein, in an orientation intended during use, the cathode body is resting on the spacing elements (48) by means of gravity.

Arrangement according to any one of the preceding claims, further comprising a support structure (62) provided with a confining arrangement (64) for confining the focusing electrode (40) and/or the cathode body (22) with respect to the support structure.

Arrangement according to claim 7, wherein the confining arrangement comprises end stops (65a, 65b) each facing a surface area of the cathode arrangement.

Arrangement according to any one of the preceding claims, wherein the cathode body houses a thermionic cathode comprising an emission portion (30) provided with the emission surface (32) for emitting electrons, and a reservoir (38) for holding a material, wherein the material, when heated, releases work function lowering particles (70) that diffuse towards the emission portion and emanate at the emission surface at a first evaporation rate ( c).

Arrangement according to claim 9, wherein the focusing electrode (40) comprises a focusing-surface (42) for focusing electrons emitted from the emission surface and an adjustable heat source configured for keeping the focusing surface of the focusing electrode at a temperature (Te) at which accumulation of work function lowering particles on the focusing surface is prevented.

Arrangement according to claim 10, wherein the focusing electrode (40) further comprises a heat trapping surface (52) facing at least a portion of the cathode body 39

(22) and arranged for receiving heat radiation (Q) emitted by the cathode body during use, and wherein the heat trapping surface is in thermal communication with the focusing surface (42).

12. Arrangement according to claim 10 or 1 1, wherein the adjustable heat source is configured for heating the cathode body and wherein preferably the focusing surface (42) is heated mainly via thermal radiation from the cathode body (22).

13. Arrangement according to claim 11 or 12, wherein the focusing electrode (40) comprises a shell (54) that surrounds the cathode body (22), the shell being provided with an inner surface, the inner surface or a portion thereof forming the heat trapping surface (52).

14. Arrangement according to any one of the preceding claims, wherein the cathode body and the focusing electrode are arranged such that direct thermal conduction from the cathode to the focusing electrode is avoided or at least minimized

15. Arrangement according to any one of claims 11 to 14, wherein a radial interspacing (58) is defined between the heat trapping surface (52) and an outer surface (36) of the cathode body (22).

16. Arrangement according to any one of claims 10 to 15, wherein the work function lowering particles (70) comprise Barium (Ba).

17. Arrangement according to claim 16, wherein the adjustable heat source (50) is configured for keeping the focusing surface temperature (Te) above 900 K.

18. Arrangement according to claim 16 or 17, wherein the adjustable heat source (50) is further configured for keeping the focusing surface temperature below 1300K. 40

19. Arrangement according to any one of claims 10 to 18, wherein the focusing surface (42) is provided with a coating suppressing electron emission.

20. Arrangement according to any one of claims 10 to 19, wherein the adjustable heat source (50) is arranged for heating the reservoir (38) such that the work function lowering particles (70) diffuse towards the emission portion (30) and emanate at the emission surface (32) at the first evaporation rate (<Dc).

21. Arrangement according to any one of claims 10 to 20, wherein the adjustable heat source comprises a heater cathode (50).

22. Arrangement according to any one of claims 10 to 21, wherein the adjustable heat source (50) is arranged within the cathode body (22) or within a receptacle (25) formed by the cathode body.

23. Arrangement according to any one of claims 1 1 or 16-19, wherein the adjustable heat source is arranged to directly heat the focusing electrode.

24. Electron gun (2) for generating an electron beam (4), the electron gun comprising:

- a cathode arrangement (20) according to any one of claims 1 - 23 for generating a plurality of electrons; and

- at least one shaping electrode (6a - 6c) for shaping the generated electrons into the electron beam.

25. Electron gun according to claim 24, comprising at least two shaping electrodes (6a

- 6c) forming an aligned electrode assembly (12), the shaping electrodes each comprising a conducting body provided with a shaping aperture (10a - 10c), the shaping apertures being coaxially aligned.

26. Electron beam lithography system (1) for exposing a target (18) using at least one electron beamlet (5), the system comprising: 41

- a beamlet generator (2, 12, 13) for generating the at least one electron beamlet;

- a beamlet modulator (14, 15) for patterning the at least one electron beamlet to form at least one modulated beamlet;

- a beamlet projector (16, 17) for projecting the at least one modulated beamlet onto a surface of the target;

wherein the beamlet generator comprises an electron gun (2) according to any one of claims 24 or 25.