Backside illumination sensor having a bonding pad structure and method of making the same
The present disclosure provides one embodiment of a semiconductor structure. The semiconductor structure comprises a device substrate having a front side and a back side; an interconnect structure disposed on the front side of the device substrate; and a bonding pad connected to the interconnect structure. The bonding pad comprises a recessed region in a dielectric material layer; a dielectric mesa of the dielectric material layer interposed between the recessed region; and a metal layer disposed in the recessed region and on the dielectric mesa.
1. A method of fabricating a semiconductor device, comprising:
forming a radiation sensor in a front side of a device substrate;
forming, on the front side of the device substrate, an interconnect structure coupled with the radiation sensor;
bonding a carrier substrate to a back side of the device substrate;
etching a dielectric material layer on the back side of the device substrate, forming an opening extending through a dielectric material layer to expose a metal feature of the interconnect structure, thereby defining a dielectric mesa of the dielectric material layer surrounded by the opening, wherein etching the dielectric material layer comprises forming a first trench and a second trench interposed by the dielectric mesa; and
forming a metal layer in the opening and on the dielectric mesa, resulting in a bonding pad, the bonding pad directly contacting the metal feature within the opening.
2. The method of claim 1 , wherein the first and second trenches completely surround the dielectric mesa.
3. The method of claim 1 , forming a shallow trench isolation structure over the dielectric material layer, and
wherein forming the opening extending through the dielectric material layer to expose the metal feature of the interconnect structure includes forming the opening through the shallow trench isolation structure.
4. A semiconductor structure, comprising:
a device substrate having a front side and a back side;
an interconnect structure disposed on the front side of the device substrate; and
a bonding pad connected to the interconnect structure, wherein the bonding pad comprises:
a recessed region in a dielectric material layer, wherein the recessed region comprises a first trench and a second trench formed in the dielectric material layer;
a dielectric mesa of the dielectric material layer interposed between the recessed region, wherein the dielectric mesa is interposed between the first and second trenches; and
a metal layer disposed in the recessed region and on the dielectric mesa.
5. The semiconductor structure of claim 1 , wherein the first and second trenches surround the dielectric mesa.
6. The semiconductor structure of claim 1 , wherein the metal layer comprises aluminum copper alloy.
7. The semiconductor structure of claim 1 , wherein the metal layer contacts a metal feature of the interconnection structure within the recessed region.
8. The semiconductor structure of claim 7 , wherein the dielectric material layer comprises:
an interlayer dielectric layer (ILD) adjacent the metal feature; and
a trench isolation feature adjacent the ILD.
9. The semiconductor structure of claim 8 , wherein the first and second trenches extend through the trench isolation feature and the ILD.
10. The semiconductor structure of claim 7 , wherein the metal feature comprises a metal line in a metal one layer.
11. The semiconductor structure of claim 1 , wherein the dielectric material layer comprises silicon oxide.
12. The semiconductor structure of claim 1 , further comprising a bonding ball disposed on the metal layer and substantially landing on a portion of the metal layer within the dielectric mesa.
13. The semiconductor structure of claim 1 , further comprising
a radiation sensing region comprising a backside illumination sensor disposed in the front side of the device substrate, the backside illumination sensor being operable to sense radiation projected toward the radiation-sensing region from the back side of the device substrate;
a radiation shield region adjacent the radiation sensing region and having a shield feature that comprises metal and is disposed on the back side of the device substrate; and
a bonding region comprising the bonding pad.
14. The semiconductor structure of claim 13 , further comprising:
a passivation layer disposed on the front side of the device substrate, wherein
the passivation layer is formed in the first and second trenches and on the dielectric mesa, and
the passivation layer is formed on the radiation shield feature.
15. The method of claim 4 , wherein a sidewall of the first trench is defined by a first sidewall of the dielectric mesa and a sidewall of the second trench is defined by a second sidewall of the dielectric mesa that opposes the first sidewall of the dielectric mesa.
16. The method of claim 15 , wherein the metal layer is disposed on the first and second sidewalls of the dielectric mesa and on a topmost surface of the dielectric mesa, the topmost surface of the dielectric mesa positioned between the first and second sidewalls of the dielectric mesa.
17. A semiconductor structure, comprising:
a semiconductor substrate having a radiation sensing region and a bonding region and having a front side and a back side;
a radiation sensor formed in the back side of the semiconductor substrate within the radiation sensing region;
an interconnect structure disposed on the front side of the semiconductor substrate and coupling the radiation sensor to a metal feature of the interconnect structure in the bonding region;
a carrier substrate bonded to the front side of the semiconductor substrate with the interconnect structure sandwiched between the semiconductor substrate and the carrier substrate;
an opening on the back side of the semiconductor substrate, wherein the opening is formed in the bonding region, extends through a dielectric material layer to the metal feature of the interconnect structure, and defines a dielectric mesa of the dielectric material layer overlying the metal feature, wherein the opening includes a first trench adjacent a first sidewall of the dielectric mesa and a second trench adjacent a second sidewall of the dielectric mesa, wherein the first sidewall of the dielectric mesa opposes the second sidewall of the dielectric mesa; and
a metal layer partially filling the opening on the back side of the semiconductor substrate in the bonding region, wherein the metal layer has direct contact with the metal feature of the interconnect structure and further extends to the dielectric mesa.
18. The semiconductor structure of claim 17 further comprising a bonding ball landing on the metal layer and vertically aligned with the dielectric mesa, wherein the radiation sensor comprises a backside illumination imaging sensor.
19. The semiconductor structure of claim 17 , wherein
the dielectric mesa is interposed between the first and second trenches.
20. The semiconductor structure of claim 17 , further comprising:
a passivation layer disposed on the backside of the semiconductor substrate, disposed in the opening of the dielectric layer and including an opening, wherein the opening of the passivation layer is aligned with the dielectric mesa and exposes the dielectric mesa.