High harmonic generation radiation source

1. A radiation source arrangement operable to cause an interaction between a drive radiation beam and a medium for generation of emitted radiation by high harmonic generation, the arrangement comprising:

an interaction region positioned at an interaction plane and configured to receive the medium;

a beam block positioned upstream of the interaction plane at a beam block plane and configured to partially block the drive radiation beam;

a beam shaper positioned upstream of the beam block plane at an object plane and configured to control a spatial distribution of the drive radiation beam; and

at least one lens positioned upstream of the interaction plane and downstream of the beam block plane, wherein the lens being positioned such that an image of the spatial distribution of the drive radiation beam is formed at the interaction plane,

wherein the beam shaper comprises a spatial light modulator (SLM), a flattop beam shaper, a deformable mirror, or a combination thereof, and

wherein the beam shaper is configured to control the spatial distribution of the drive radiation beam such that the drive radiation beam is a non-Gaussian beam at the object plane.

2. The arrangement of claim 1 , wherein the lens is positioned such that the object plane and the interaction plane are conjugate planes.

3. The arrangement of claim 1 , wherein an aperture is positioned downstream of the interaction plane at an aperture plane and configured to allow at least part of the emitted radiation to pass through and to block at least part of the drive radiation beam, wherein the aperture plane is positioned with respect to the beam block plane and the lens such that an image of the beam block is formed at the aperture plane.

4. The arrangement of claim 3 , wherein the lens is positioned such that the beam block plane and the aperture plane are conjugate planes.

5. The arrangement of claim 3 , wherein a dimension of the beam block in the beam block plane relative to a dimension of the drive radiation beam in the beam block plane is such that the image of the beam block and the image of the spatial distribution of the drive radiation beam are decoupled.

6. The arrangement of claim 5 , wherein the dimension of the beam block in the beam block plane is 30% or less of the dimension of the drive radiation beam in the beam block plane.

7. The arrangement of claim 6 , wherein the beam block and the drive radiation beam have substantially circular cross sections in the beam block plane, and wherein the dimensions of the beam block and the drive radiation beam are diameters.

8. The arrangement of claim 3 , wherein a depth of focus of the image of the beam block does not overlap the interaction plane.

9. The arrangement of claim 8 , wherein a center of the depth of focus of the image of the beam block is substantially coincident with the aperture plane.

10. The arrangement of claim 8 , wherein a circle of confusion associated with the depth of focus of the image of the beam block is larger than the image of the drive radiation beam at the interaction plane.

11. The arrangement of claim 10 , wherein the depth of focus of the image of the beam block has a maximum circle of confusion having a diameter of 35 μm or less.

12. The arrangement of claim 1 , wherein a depth of focus of the image of the spatial distribution of the drive radiation beam does not overlap an aperture plane of an aperture positioned downstream of the interaction plane.

13. The arrangement of claim 12 , wherein a center of the depth of focus of the image of the spatial distribution of the drive radiation beam is substantially coincident with the interaction plane.

14. The arrangement of claim 8 , wherein at least one of the depth of focus of the image of the beam block and the depth of focus of the image of the spatial distribution of the drive radiation beam is determined by

Depth of focus=2 cN (1+ m )

where c is a maximum circle of confusion, N is a ratio of focal length of the lens to a diameter of the drive radiation beam at the lens, and m is a magnification factor of the image of the beam block at the aperture plane.

15. The arrangement of claim 1 , further comprising a sensor configured to detect a spatial profile of the drive radiation beam at the interaction plane; and

a feedback controller configured to feedback data relating to the detected spatial profile of the drive radiation beam to the beam shaper,

wherein the beam shaper is configured to control the spatial profile of the drive radiation beam based on the data fed back.

16. A metrology apparatus comprising:

an arrangement operable to cause an interaction between a drive radiation beam and a medium for generation of emitted radiation by high harmonic generation, the arrangement comprising:

an interaction region positioned at an interaction plane and configured to receive the medium;

a beam block positioned upstream of the interaction plane at a beam block plane and configured to partially block the drive radiation beam;

a beam shaper positioned upstream of the beam block plane at an object plane and configured to control a spatial distribution of the drive radiation beam; and

at least one lens positioned upstream of the interaction plane and downstream of the beam block plane, wherein the lens being positioned such that an image of the spatial distribution of the drive radiation beam is formed at the interaction plane,

wherein the beam shaper comprises a spatial light modulator (SLM), a flattop beam shaper, a deformable mirror, or a combination thereof, and

wherein the beam shaper is configured to control the spatial distribution of the drive radiation beam such that the drive radiation beam is a non-Gaussian beam at the object plane.

17. A lithographic cell comprising the metrology apparatus according to claim 16 .

18. A method of causing an interaction between a drive radiation beam and a medium, for generation of emitted radiation by high harmonic generation, the method comprising:

shaping the drive radiation beam with a beam shaper to control a spatial distribution of the drive radiation beam, wherein the beam shaper comprises a spatial light modulator (SLM), a flattop beam shaper, a deformable mirror, or a combination thereof, and wherein the beam shaper is configured to control the spatial distribution of the drive radiation beam such that the drive radiation beam is a non-Gaussian beam at the object plane;

blocking the drive radiation beam with a beam block positioned downstream of the beam shaper such that at least part of the drive radiation beam is blocked;

propagating the drive radiation beam through at least one lens positioned downstream of the beam block;

impinging the drive radiation beam on an interaction region comprising the medium and positioned downstream of the beam block; and

focusing the drive radiation at an aperture positioned downstream of the interaction region at an aperture plane such that an image of the beam block is formed at the aperture plane, the aperture being configured to allow at least part of the emitted radiation to pass through and to block at least part of the drive radiation beam.

19. A radiation source arrangement operable to cause an interaction between a drive radiation beam and a medium for generation of emitted radiation by high harmonic generation, the arrangement comprising:

an interaction region positioned at an interaction plane and configured to receive the medium;

a beam block positioned upstream of the interaction plane at a beam block plane and configured to partially block the drive radiation beam;

a beam shaper positioned upstream of the beam block plane at an object plane and configured to control a spatial distribution of the drive radiation beam; and

at least one lens positioned upstream of the interaction plane and downstream of the beam block plane, wherein the lens being positioned such that an image of the spatial distribution of the drive radiation beam is formed at the interaction plane,

wherein the beam shaper is configured to control the spatial distribution of the drive radiation beam such that the drive radiation beam is a non-Gaussian beam at the object plane.