Wafer alignment system with optical coherence tomography

1. A system for performing alignment of two wafers, comprising:

an optical coherence tomography system; and

a wafer alignment system;

wherein the wafer alignment system is configured and disposed to control the relative position of a first wafer and a second wafer, and wherein the optical coherence tomography system is configured and disposed to compute three-dimensional coordinate data for a plurality of alignment marks on the first wafer and second wafer; and send said coordinate data to the wafer alignment system.

2. The system of claim 1 , wherein the optical coherence tomography system comprises a light source that emits light having a wavelength ranging between 1.1 micrometers and 1.7 micrometers.

3. The system of claim 1 , wherein each of the plurality of alignment marks comprises a silicon region surrounded by a film region.

4. The system of claim 3 , wherein the film region comprises an oxide region.

5. The system of claim 3 , wherein the film region comprises a nitride region.

6. The system of claim 3 , wherein the silicon region has a ring shape.

7. The system of claim 3 , wherein the silicon region has a rectangle shape.

8. The system of claim 3 , wherein the silicon region has a cross shape.

9. The system of claim 3 , wherein each of the plurality of alignment marks is positioned within a non-metal zone, and wherein the non-metal zone extends throughout the depth of the wafer.

10. The system of claim 3 , wherein the plurality of alignment marks comprises a first set of parallel marks having a first pitch, and a second set of parallel marks having a second pitch, wherein the second pitch is smaller than the first pitch.

11. A system for performing alignment of two wafers, comprising:

a light source configured to emit light having a wavelength ranging between 1.1 micrometers and 1.7 micrometers;

a collimating lens configured and disposed to collimate light from said light source;

a beam splitter configured and disposed to split the light from said collimating lens into a reference path and a target path;

an objective lens configured and disposed to focus light of the target path onto a set of wafers comprising a first wafer and a second wafer;

a detector configured and disposed to receive light from the reference path and the target path;

a computer system configured and disposed to compute a three-dimensional tomogram of the set of wafers and compute three-dimensional correction data; and

a wafer stage control configured and disposed to receive correction data from the computer system and adjust the relative position of the first wafer and second wafer in response to said correction data.

12. A method for performing alignment of two wafers, the two wafers comprising a first wafer and a second wafer, comprising:

obtaining a three-dimensional tomogram of the two wafers;

computing three-dimensional alignment correction data;

sending the alignment correction data to a wafer stage control; and

adjusting the relative position of the two wafers with the wafer stage control in response to receiving said alignment data.

13. The method of claim 12 , wherein computing alignment correction data comprises:

identifying a first alignment mark on the first wafer and recording its location in X, Y, and Z dimensions;

identifying a second alignment mark on the second wafer and recording its location in X, Y, and Z dimensions; and

computing the difference between the first alignment mark and the second alignment mark in X, Y, and Z dimensions.

14. The method of claim 13 , further comprising:

identifying at least three alignment marks on the first wafer and recording their locations in X, Y, and Z dimensions;

identifying at least three alignment marks on the second wafer and recording their locations in X, Y, and Z dimensions;

computing the best-fit plane for the alignment marks on the first wafer; and

computing the best-fit plane for the alignment marks on the second wafer.

15. The method of claim 14 , further comprising adjusting the relative orientations of the first wafer so that the best fit plane for the alignment marks on the first wafer is parallel to the best-fit plane for the alignment marks on the second wafer.

16. The method of claim 13 , further comprising:

identifying at least four alignment marks on the first wafer and recording their locations in X, Y, and Z dimensions;

identifying at least four alignment marks on the second wafer and recording their locations in X, Y, and Z dimensions;

computing a best-fit residual to a plane for the four alignment marks on the first wafer;

computing a best-fit residual to a plane for the four alignment marks on the second wafer; and

rejecting the first wafer or the second wafer in response to a corresponding best-fit residual that exceeds a predetermined value.

17. The method of claim 13 , wherein identifying a first alignment mark and identifying a second alignment mark comprises identifying a horizontal bar.

18. The method of claim 13 , wherein identifying a first alignment mark and identifying a second alignment mark comprises identifying a vertical bar.

19. The method of claim 13 , wherein identifying a first alignment mark and identifying a second alignment mark comprises identifying a diagonal bar.

20. The method of claim 12 , further comprising:

identifying a first set of parallel marks having a first pitch; and

identifying a second set of parallel marks having a second pitch, wherein the second pitch is smaller than the first pitch.