Apparatus and method for verification of bonding alignment

1. A device comprising:

a common node disposed in a first wafer;

a test node disposed in the first wafer and having a plurality of test pads exposed at a first surface of the first wafer, the test node further having a plurality of test node lines separated by a first spacing and extending to a second surface of the first wafer and each connected to a respective one of the plurality of test pads; and

a comb disposed in a second wafer and having a plurality of comb lines having a second spacing different from the first spacing, each of the comb lines having a first surface exposed at a first side of the second wafer, the comb lines configured to provide an indication of an alignment of the first wafer with the second wafer by a number or arrangement of connections made by the plurality of comb lines between the test node lines and the common node.

2. The device of claim 1 , wherein the second spacing is greater than the first spacing.

3. The device of claim 1 , wherein the comb is a Vernier-type comb.

4. The device of claim 3 , wherein the test node has a same number of test node lines as a number of comb lines.

5. The device of claim 3 , wherein the comb lines are arranged to have a single comb line aligning directly with a corresponding test line at predetermined alignment shifts.

6. The device of claim 1 , wherein the comb is a binary comb.

7. The device of claim 1 , wherein the comb lines are spaced laterally apart, and the first surface of each of the comb lines has a lateral width between about 0.005 μm and about 0.2 μm.

8. The device of claim 1 , wherein a portion of the test node and a portion of the common node are disposed in a redistribution layer (RDL) on the first wafer.

9. The device of claim 8 , wherein the comb is disposed in an RDL on the second wafer.

10. A device comprising:

a first wafer having a common node extending from a first side of the first wafer to a second side, the first wafer further having a test node having a plurality of test node lines each extending from the first side of the first wafer to the second side; and

a second wafer having a comb having a plurality of comb lines, each of the comb lines having a first portion and a second portion each disposed at a first side of the second wafer;

wherein the first wafer is bonded at a second side to a first side of the second wafer; and

wherein the comb is configured to create an number of connections and connection arrangements between the common node and test node that indicate an alignment shift of the first wafer in relation to the bonded second wafer.

11. The device of claim 10 , wherein the comb lines are configured to provide, at one of a plurality of predetermined alignment shifts, electrical connections between the common node and one or more test lines when the first wafer is bonded to the second wafer.

12. The device of claim 11 , wherein the comb is a Vernier-type comb.

13. The device of claim 11 , wherein the comb is a binary comb.

14. The device of claim 10 , wherein the comb lines are spaced laterally apart, wherein the first portion of each of the comb lines has a lateral width between about 0.005 μm and about 0.2 μm.

15. The device of claim 10 , wherein the comb lines are spaced laterally apart, wherein the test lines have a first surface of the first portion disposed at the first side of the second wafer, and wherein the first surface of each test node line has a lateral width of about 0.01 μm.

16. The device of claim 10 , wherein a portion of the test node and a portion of the common node are disposed in a redistribution layer (RDL) on the first wafer, and wherein the comb is disposed in an RDL on the second wafer.

17. The device of claim 16 , wherein the test node and the common node are disposed in a dicing street on the first wafer, and wherein the comb is disposed in a dicing street on the second wafer.

18. A method, comprising

providing a top wafer having a common node extending from a first side to a second side and a test node extending from the first side to the second side, the test node having a plurality of test node lines spaced apart by a first separation distance;

providing a bottom wafer having a comb, the comb having a plurality of comb lines spaced apart by a second separation distance different than the first separation, each of the comb lines having a first portion and a second portion disposed at a first surface of the bottom wafer, and wherein a location of the comb in the bottom wafer corresponds to locations of the common node and the test node in the top wafer;

bonding the second side of the top wafer to the first side of the bottom wafer to form a wafer bond; and

determining an alignment shift of the wafer bond by determining a number or arrangement of connections between the common node and the test node by the comb.

19. The method of claim 18 , wherein the comb is a Vernier-type comb, and wherein the determining the alignment shift comprises checking for an electrical connection between the common node and each of the plurality of test node lines and determining the alignment shift based on which test node exhibits the electrical connection with the common node.

20. The method of claim 18 , wherein the comb is a binary comb, and wherein the determining the alignment shift comprises checking for a combination of electrical connections between the common node and each of the plurality of test node lines and determining the alignment shift from the combination of electrical connections.