Metrology apparatus

1. A metrology tool for determining a parameter of interest of a structure fabricated on a substrate, the metrology tool comprising:

an illumination optical system configured to illuminate the structure with illumination radiation under non-zero angles of incidence;

a detection optical system comprising:

at least one lens configured to direct a portion of illumination radiation scattered by the structure; and a detection optical sensor configured to receive the directed portion of illumination radiation scattered by the structure and to generate image information of the structure,

wherein the illumination optical system and the detection optical system do not share an optical element, and

wherein at least part of an optical axis of the illumination optical system is substantially parallel to an optical axis of the detection optical system; and

a computational imaging processor configured to:

receive aberration information of the at least one lens and the generated image information; and

adjust the image information based on the aberration information.

2. The metrology tool of claim 1 , wherein at least part of the illumination optical system is positioned radially outwards from a radial extent of the detection optical system.

3. The metrology tool of claim 1 , wherein the illumination optical system comprises at least one mirror for reflecting illumination radiation from a corresponding one of the at least two fiber optics towards the structure.

4. The metrology tool of claim 3 , comprising at least one mirror in one or more of a plurality of optical paths.

5. The metrology tool of claim 3 , wherein the at least one mirror is configured to direct the illumination radiation onto the structure through a volume between at least one lens of the detection optical system and the substrate.

6. The metrology tool of claim 3 , wherein the at least one mirror is configured to direct radiation having a plurality of wavelengths in a range from 200 nm to 2 μm to substantially the same point on the substrate.

7. The metrology tool of claim 3 , wherein the at least one mirror is one of an elliptical or a parabolic mirror.

8. The metrology tool of claim 1 , wherein the detection optical system has a total transmissivity of greater than 90%.

9. The metrology tool of claim 1 , wherein the detection optical system comprises at least one of: a plano-convex lens; an aspheric lens; a bispherical lens; a bi-aspheric lens and a long working distance objective.

10. The metrology tool of claim 1 , further comprising a focus system comprising at least one focusing optical sensor configured to receive zeroth order radiation reflected from the structure, wherein the computational imaging processor is further configured to determine a focus of the detection optical system based on focus information received from the at least one focusing optical sensor and to adjust the image information based on the focus information.

11. The metrology tool of claim 1 , further comprising a polarization element arranged around an outer portion of the detection optical system and configured to interact with radiation propagating through the illumination optical system for polarization thereof.

12. The metrology tool of claim 1 , further comprising a shutter system positioned in at least one of the plurality of optical paths configurable between an open position in which illumination radiation is allowed to pass and a closed position in which illumination radiation is blocked.

13. The metrology tool of claim 1 , wherein the illumination optical system and the detection optical system together have a footprint less than the area of a field of the substrate.

14. The metrology tool of claim 1 , wherein the illumination optical system comprises at least two optical fibers configured to guide the illumination radiation to the structure.

15. The metrology tool of claim 1 , wherein a cross-sectional diameter of a combination of the illumination optical system and the detection optical system is smaller than 50 mm.

16. The metrology system of claim 1 , wherein the adjusting the image information based on the aberration information comprises enhancing a dark field image determined from the image information.

17. The metrology system of claim 1 , wherein:

the at least one lens is further configured to transmit a plurality of wavelengths of the portion of illumination radiation scattered by the structure;

the at least one lens has associated aberrations in the plurality of wavelengths; and

the adjusting of the image information based on the aberration information comprises correcting effects of the associated aberrations on the image information.

18. A metrology tool for determining a parameter of interest of a structure fabricated on a substrate, the metrology tool comprising:

an illumination optical system configured to illuminate the structure with illumination radiation under non-zero angles of incidence;

a detection optical system comprising:

at least one lens configured to direct a portion of illumination radiation scattered by the structure; and a detection optical sensor configured to receive the directed portion of illumination radiation scattered by the structure and to generate image information of the structure,

wherein the illumination optical system and the detection optical system do not share an optical element,

wherein the illumination optical system comprises a plurality of discrete optical paths, and

wherein at least two of the plurality of optical paths are diametrically opposed when incident on the structure; and

a computational imaging processor configured to:

receive aberration information of the at least one lens and the generated image information; and

adjust the image information based on the aberration information.