Simultaneous capturing of overlay signals from multiple targets
Metrology methods and systems are provided, in which the detected image is split at a field plane of the collection path of the metrology system's optical system into at least two pupil plane images. Optical elements such as prisms may be used to split the field plane images, and multiple targets or target cells may be measured simultaneously by spatially splitting the field plane and/or the illumination sources and/or by using two polarization types. The simultaneous capturing of multiple targets or target cells increases the throughput of the disclosed metrology systems.
1. A metrology system comprising:
an optical system with an illumination path and a collection path, with at least one detector at a pupil plane of the collection path, wherein the optical system comprises at least one optical element at at least one field plane of the collection path thereof which is configured to split a detected image into at least two pupil plane images, wherein the field plane is optically conjugate in the optical system to a target on a wafer, and wherein the pupil plane is equivalent to a Fourier plane with respect to the target on the wafer.
2. The metrology system of claim 1 , wherein the at least two pupil plane images are detected by a single detector of the system.
3. The metrology system of claim 1 , wherein the at least two pupil plane images are detected by at least two corresponding detectors of the system.
4. The metrology system of claim 1 , wherein the at least two pupil plane images comprise at least four pupil plane images corresponding to at least four targets which are captured simultaneously by the system.
5. The metrology system of claim 1 , wherein the illumination path comprises two perpendicularly polarized illumination sources and the at least two pupil plane images are detected by at least two corresponding detectors of the system.
6. The metrology system of claim 1 , wherein the illumination path and the collection path are polarized, the illumination path comprising two perpendicularly polarized illumination sources and the collection path comprising two perpendicularly polarized detectors, each detecting at least two pupil plane images generated from correspondingly polarized illumination.
7. The metrology system of claim 6 , wherein each of the two perpendicularly polarized illumination sources comprises at least two illumination sources which are spatially separated in the field plane of the illumination path.
8. The metrology system of claim 7 , wherein the at least two illumination sources are at different wavelength ranges.
9. The metrology system of claim 6 , further comprising at least one scanner configured to scan at least one of the illumination sources within at least one target cell.
10. The metrology system of claim 6 , further comprising apodizing apertures at the pupil plane of the illumination path.
11. The metrology system of claim 1 , further comprising at least one zeroth order blocker at a pupil plane in the collection path.
12. A method comprising:
splitting a detected image at a field plane of a collection path of a metrology system's optical system into at least two pupil plane images, wherein the field plane is optically conjugate in the optical system to a target on a wafer.
13. The method of claim 12 , further comprising capturing the at least two pupil plane images simultaneously by at least one detector of the metrology system.
14. The method of claim 12 , further comprising detecting the at least two pupil plane images by a single detector.
15. The method of claim 12 , further comprising detecting the at least two pupil plane images by at least two corresponding detectors.
16. The method of claim 12 , wherein the at least two pupil plane images comprise at least four pupil plane images corresponding to at least four targets which are captured simultaneously by the metrology system.
17. The method of claim 12 , further comprising configuring an illumination path of the optical system to have two perpendicularly polarized illumination sources and further comprising detecting the at least two pupil plane images by at least two corresponding detectors.
18. The method of claim 12 , further comprising polarizing an illumination path and the collection path of the optical system, by configuring the illumination path to comprise two perpendicularly polarized illumination sources and configuring the collection path to comprise two perpendicularly polarized detectors, and further configuring each of the detectors to detect at least two pupil plane images generated from correspondingly polarized illumination.
19. The method of claim 18 , wherein the two perpendicularly polarized illumination sources are at different wavelength ranges.
20. The method of claim 18 , further comprising configuring each of the two perpendicularly polarized illumination sources to comprise at least two illumination sources which are spatially separated in the field plane of the illumination path.
21. The method of claim 18 , further comprising scanning at least one of the illumination sources within at least one target cell.
22. The method of claim 12 , further comprising blocking zeroth diffraction orders at a pupil plane in the collection path.
23. The method of claim 12 , further comprising underfilling the target on the wafer during illumination of the target.