Bonding structures and methods for forming the same
A bonding structure is provided, including a first substrate; a second substrate disposed opposite the first substrate; a first bonding layer disposed on the first substrate; a second bonding layer disposed on the second substrate and opposite the first bonding layer; and a silver feature disposed between the first bonding layer and the second bonding layer. The silver feature includes a silver nano-twinned structure including parallel twin boundaries. The silver nano-twinned structure includes 90% or more [111] crystal orientation. A method for forming a bonding structure is also provided. Each of steps of forming a first silver feature and second silver feature includes sputtering or evaporation coating. Negative bias ion bombardment is applied to the first silver feature and second silver feature during sputtering or evaporation.
1. A bonding structure, comprising:
a first substrate;
a second substrate disposed opposite the first substrate;
a first bonding layer disposed on the first substrate;
a second bonding layer disposed on the second substrate and opposite the first bonding layer; and
a silver feature disposed between the first bonding layer and the second bonding layer, wherein the silver feature comprises a silver nano-twinned structure comprising parallel twin boundaries, wherein the parallel twin boundaries comprise 90% or more [111] crystal orientation.
2. The bonding structure as claimed in claim 1 , wherein a thickness of the silver feature is at least 0.3 μm.
3. The bonding structure as claimed in claim 1 , wherein a thickness of the silver nano-twinned structure is at least 0.1 μm.
4. The bonding structure as claimed in claim 1 , wherein a distance between the parallel twin boundaries is between 1 nm and 100 nm.
5. The bonding structure as claimed in claim 1 , wherein the silver feature further comprises:
a first transition grain layer between the first bonding layer and the silver nano-twinned structure; and
a second transition grain layer between the second bonding layer and the silver nano-twinned structure.
6. The bonding structure as claimed in claim 5 , wherein the silver feature comprises 70% or more [111] crystal orientation.
7. The bonding structure as claimed in claim 1 , further comprising:
a first via in the first substrate and connected to the first bonding layer; and
a second via in the second substrate and connected to the second bonding layer.
8. The bonding structure as claimed in claim 1 , wherein each of the first substrate and the second substrate comprises a silicon (Si) chip, a Si wafer, or a combination thereof.
9. The bonding structure as claimed in claim 1 , wherein each of the first bonding layer and the second bonding layer comprises copper (Cu), aluminum (Al), silver (Ag), nickel (Ni), titanium (Ti), chromium (Cr), Cu/Ti, Cu/Ni, Cu/Cr or a combination thereof.
10. A method for forming a bonding structure, comprising:
forming a first bonding layer on a first substrate;
forming a first silver feature on the first bonding layer;
forming a second bonding layer on a second substrate;
forming a second silver feature on the second bonding layer; and
bonding the first silver feature and the second silver feature to form a third silver feature between the first bonding layer and the second bonding layer, wherein the third silver feature comprises a silver nano-twinned structure comprising parallel twin boundaries, wherein the parallel twin boundaries comprise 90% or more [111] crystal orientation.
11. The method as claimed in claim 10 , wherein a thickness of the third silver feature is at least 0.3 μm, a thickness of the silver nano-twinned structure is at least 0.1 μm and a distance between the parallel twin boundaries is between 1 nm and 100 nm.
12. The method as claimed in claim 10 , wherein each of the steps of forming the first silver feature and the second silver feature comprises sputtering or evaporation coating, wherein a negative bias with a voltage of 0 to −300 V and a current of about 0 to about 3.0 A is applied to the first silver feature and the second silver feature during the sputtering or evaporation coating.
13. The method as claimed in claim 10 , wherein the bonding of the first silver feature and the second silver feature is performed at a temperature between 100° C. and 250° C.
14. The method as claimed in claim 10 , wherein the bonding of the first silver feature and the second silver feature is performed at a pressure between 1 MPa and 30 MPa.
15. The method as claimed in claim 10 , wherein the bonding of the first silver feature and the second silver feature is performed at a vacuum of 10 −3 torr or higher.
16. The method as claimed in claim 10 , wherein period of the bonding of the first silver feature and the second silver feature is between 10 minutes and 60 minutes.
17. The method as claimed in claim 10 , further comprising:
forming a first transition grain layer between the first bonding layer and the silver nano-twinned structure; and
forming a second transition grain layer between the second bonding layer and the silver nano-twinned structure.
18. The method as claimed in claim 17 , wherein the third silver feature comprises the first transition grain layer, the second transition grain layer and the silver nano-twinned structure, and the third silver feature comprises 70% or more [111] crystal orientation.
19. The method as claimed in claim 10 , further comprising:
forming a first via in the first substrate, wherein the first via is connected to the first bonding layer; and
forming a second via in the second substrate, wherein the second via is connected to the second bonding layer.
20. The method as claimed in claim 10 , wherein each of the first substrate and the second substrate comprises a Si chip, a Si wafer, or a combination thereof and each of the first bonding layer and the second bonding layer comprises copper (Cu), aluminum (Al), silver (Ag), nickel (Ni), titanium (Ti), chromium (Cr), Cu/Ti, Cu/Ni, Cu/Cr or a combination thereof.