Tilted slit confocal system configured for automated focus detection and tracking
A system for automated focus tracking of a sample is disclosed. The system comprises an illumination source, a set of illumination optics in an illumination path, a set of collection optics in a collection path, a first slit device in the illumination path, a second slit device in the collection path, at least one detector configured to generate an image of the sample, and a controller configured to receive through-focus information from the image, and provide corrective motion to a stage holding the sample to maintain a position of the sample at a selected focus. A method for automated focus tracking of a sample is also disclosed.
1. An optical characterization system, comprising:
an illumination source;
a set of illumination optics in an illumination path configured to illuminate a sample with illumination from the illumination source;
a set of collection optics in a collection path;
a first slit device in the illumination path located at a first plane conjugate to the sample;
a second slit device in the collection path located at a second plane conjugate to the sample,
wherein at least one of the first slit device is tilted with respect to an optical axis of the illumination path or the second slit device is tilted with respect to an optical axis of the collection path;
at least one detector configured to generate an image of the sample, wherein the image includes data associated with the first slit device and the second slit device; and
a controller configured to be communicatively coupled with the at least one detector, the controller including one or more processors configured to execute program instructions causing the one or more processors to:
receive through-focus information from the data associated with the first slit device and the second slit device, and
provide corrective motion to a stage holding the sample to maintain a position of the sample at a selected focus.
2. The optical characterization system of claim 1 , wherein at least one of the first slit device is normal with respect to the optical axis of the illumination path or the second slit device is normal with respect to the optical axis of the collection path.
3. The optical characterization system of claim 1 , wherein the selected focus is at a focus offset of zero or a selected non-zero value.
4. The optical characterization system of claim 1 , wherein an aperture placed at a pupil in the illumination path comprises a full open aperture, a half open aperture, a ring aperture, a center blocked aperture, a dipole aperture, or a slit aperture.
5. The optical characterization system of claim 1 , wherein the sample is a semiconductor wafer, a reticle, or a photomask.
6. The optical characterization system of claim 1 , wherein the set of illumination optics comprises:
at least one of a lens, a mirror, a beam splitter, or a prism mirror.
7. The optical characterization system of claim 1 , wherein the set of collection optics comprises:
at least one of a lens, a mirror, a beam splitter, or a prism mirror.
8. The optical characterization system of claim 1 , wherein at least one of the first slit device or the second slit device comprises a single slit.
9. The optical characterization system of claim 1 , wherein at least one of the first slit device or the second slit device comprises an array of slits.
10. The optical characterization system of claim 1 , wherein the at least one detector comprises a 1-D array.
11. The optical characterization system of claim 1 , wherein the at least one detector comprises a 2-D camera.
12. The optical characterization system of claim 11 , wherein the controller causes the one or more processors to receive the image from the 2-D camera and bin the image to select columns of pixels in the image.
13. The optical characterization system of claim 12 , wherein the columns of pixels have an adjustable number of pixels.
14. The optical characterization system of claim 1 , wherein the at least one detector comprises a first detector and a second detector.
15. The optical characterization system of claim 14 , wherein a beam splitter splits the collection path between a first channel and a second channel, the first channel includes the second slit device and the first detector, and the second channel includes the second detector.
16. The optical characterization system of claim 15 , wherein the first channel corresponds to a first field of view of the image, and the second channel corresponds to a second field of view of the image.
17. The optical characterization system of claim 1 , comprising a movable focusing lens configured to increase a range of a focus offset.
18. The optical characterization system of claim 1 , wherein the first slit device and the second slit device each comprise an array of pinholes.
19. An optical characterization method, comprising:
receiving through-focus information from an image of a sample generated by at least one detector of an optical characterization subsystem, wherein the optical characterization subsystem comprises:
an illumination source,
a set of illumination optics in an illumination path configured to illuminate the sample with illumination from the illumination source,
a set of collection optics in a collection path,
a first slit device in the illumination path located at a first plane conjugate to the sample,
a second slit device in the collection path located at a second plane conjugate to the sample,
wherein at least one of the first slit device is tilted with respect to an optical axis of the illumination path or the second slit device is tilted with respect to an optical axis of the collection path,
the at least one detector configured to generate the image of the sample, wherein the image includes data associated with the first slit device and the second slit device; and
providing corrective motion to a stage holding the sample to maintain a position of the sample at a selected focus.
20. The method of claim 19 , wherein at least one of the first slit device is normal with respect to the optical axis of the illumination path or the second slit device is normal with respect to the optical axis of the collection path.
21. The method of claim 19 , wherein the selected focus is at a focus offset of zero or a selected non-zero value.
22. The method of claim 19 , wherein an aperture placed at a pupil in the illumination path comprises a full open aperture, a half open aperture, a ring aperture, a center blocked aperture, a dipole aperture, or a slit aperture.
23. The method of claim 19 , wherein the sample is a semiconductor wafer, a reticle, or a photomask.
24. The method of claim 19 , wherein the set of illumination optics comprises:
at least one of a lens, a mirror, a beam splitter, or a prism mirror.
25. The method of claim 19 , wherein the set of collection optics comprises:
at least one of a lens, a mirror, a beam splitter, or a prism mirror.
26. The method of claim 19 , wherein at least one of the first slit device or the second slit device comprises a single slit.
27. The method of claim 19 , wherein at least one of the first slit device or the second slit device comprises an array of slits.
28. The method of claim 19 , wherein the at least one detector comprises a 1-D array.
29. The method of claim 19 , wherein the at least one detector comprises a 2-D camera.
30. The method of claim 29 , wherein receiving through-focus information from the image of the sample further comprises receiving the image from the 2-D camera and binning the image to select columns of pixels in the image.
31. The method of claim 30 , wherein the columns of pixels have an adjustable number of pixels.
32. The method of claim 19 , wherein the at least one detector comprises a first detector and a second detector.
33. The method of claim 32 , wherein a beam splitter splits the collection path between a first channel and a second channel, the first channel includes the second slit device and the first detector, and the second channel includes the second detector.
34. The method of claim 19 , comprising a movable focusing lens configured to increase a range of a focus offset.
35. The method of claim 19 , wherein the first slit device and the second slit device each comprise an array of pinholes.