PATENTSCOPE will be unavailable a few hours for maintenance reason on Tuesday 19.11.2019 at 4:00 PM CET
Search International and National Patent Collections
Some content of this application is unavailable at the moment.
If this situation persists, please contact us atFeedback&Contact
1. (WO2007008742) OPTIMIZING USE AND PERFORMANCE OF OPTICAL SYSTEMS IMPLEMENTED WITH TELECENTRIC ON-AXIS DARK FIELD ILLUMINATION
Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

Claims
1. An imaging system for imaging a defect on a planar specular object, the imaging system comprising:
a telecentric lens having a sufficiently aspherical surface such that the telecentric lens is substantially corrected for an optical aberration;
a telecentric stop including an aperture therein to block light reflected from the planar specular object while allowing light reflected from the defect to pass through the aperture; and
a lens group having a system stop positioned between the telecentric stop and the lens group, the lens group being substantially corrected for the optical aberration independent of the telecentric lens.

2. The imaging system of claim 1 , further comprising a camera for imaging the planar specular object through the telecentric lens, the telecentric stop, and the lens group.

3. The imaging system of claim 2 wherein the camera comprises a complementary metal-oxide semiconductor (CMOS) sensor.

4. The imaging system of claim 3 wherein the imaging system has a depth of focus of approximately ±10 mm.

5. The imaging system of claim 1 , wherein the defect is a soft mark.

6. The imaging system of claim 1 , wherein the telecentric lens comprises a molded polymer.

7. The imaging system of claim 1 , wherein the optical aberration comprises spherical aberration.

8. The imaging system of claim 1 , wherein the lens group comprises a pinhole lens.

9. The imaging system of claim 1 , further comprising a source of illumination positioned to illuminate the planar specular object along an axis of the telecentric lens.

10. The imaging system of claim 9, wherein the source of illumination comprises two or more concentric arrays of light emitting diodes (LEDs).

11. The imaging system of claim 10, wherein successive concentric arrays in the two or more concentric arrays of LEDs alternate between being tangentially arranged and radially arranged with respect to a common center point.

12. A telecentric on-axis darkfield (TOAD) lighting device comprising:
a first circular array of illumination sources arranged radially with respect to a center point, the first circular array located at a first radius from the center point; and a second circular array of illumination sources arranged tangentially with respect to the center point, the second circular array located at a second radius from the center point.

13. The TOAD lighting device of claim 12, further comprising a third circular array of illumination sources arranged radially with respect to the center point, the third circular array located at a third radius from the center point.

14. The TOAD lighting device of claim 13, further comprising a fourth circular array of illumination sources arranged tangentially with respect the center point, the fourth circular array located at a fourth radius from the center point.

15. The TOAD lighting device of claim 14, wherein the second radius is longer than the first radius.

16. The TOAD lighting device of claim 15, wherein the third radius is longer than the second radius.

17. The TOAD lighting device of claim 16, wherein the fourth radius is longer than the third radius.

18. A method for aligning a telecentric on-axis darkfield (TOAD) lighting device with a substantially specular surface, the TOAD lighting device having a plurality of concentric illumination arrays, the method comprising:
adjusting an angle of incidence between the TOAD lighting device and an object plane in a first direction until an area of intense brightness is substantially removed from a first side of an image of the specular surface;
recording the adjusted angle of incidence as a first measurement;
adjusting the angle of incidence between the TOAD lighting device and the object plane in an opposite direction as compared to the first direction until the area of intense brightness is substantially removed from a second side of the image of the specular surface;
recording the readjusted angle of incidence as a second measurement; and determining an aligned angle of incidence for the first direction as an approximate difference between the first measurement and the second
measurement.

19. The method of claim 18, wherein adjusting the angle of incidence between the TOAD lighting device and the object plane comprises:
selecting an innermost concentric illumination array; and
adjusting an angle of incidence between the innermost concentric illumination array and the TOAD lighting device.

20. The method of claim 18, further comprising:
adjusting the angle of incidence between the TOAD lighting device and an object plane in a second direction until the area of intense brightness is substantially removed from a third side of the image of the specular surface;
recording the adjusted angle of incidence as a third measurement;
adjusting the angle of incidence between the TOAD lighting device and the object plane in an opposite direction as compared to the second direction until the area of intense brightness is substantially removed from a fourth side of the image of the specular surface;
recording the readjusted angle of incidence as a fourth measurement; and determining an aligned angle of incidence for the second direction as an approximate difference between the third measurement and the fourth
measurement.

21. An imaging system for imaging a semiconductor wafer, the imaging system comprising:
means for illuminating the wafer;
means for providing an image of the wafer to a sensing means, a working distance being defined by a distance between the wafer and the means for providing the image to the sensing means; and
means for maintaining focus of the image when the working distance changes over a range of approximately ±10 mm.

22. The imaging system of claim 21 , wherein the means for illuminating the wafer provides darkfield lighting.

23. The imaging system of claim 21 , wherein the means for illuminating the wafer provides telecentric on-axis darkfield lighting.