Source/drain metal contact and formation thereof

1. A semiconductor device, comprising:

a fin disposed on a substrate;

a source/drain feature disposed over the fin;

a silicide layer disposed over the source/drain feature and extending to wrap around a bottom surface of the source/drain feature;

a seed metal layer disposed over the silicide layer and wrapping around the source/drain feature; and

a metal layer disposed over the metal seed layer.

2. The semiconductor device of claim 1 , wherein the silicide layer wraps around the source/drain feature, and wherein the seed metal layer wraps around the silicide layer.

3. The semiconductor device of claim 1 , wherein semiconductor device further includes a spacer disposed over sidewalls of the metal layer, and wherein the spacer lands on a top surface of the seed metal layer.

4. The semiconductor device of claim 1 , wherein

the fin is a first fin, wherein the semiconductor device further comprises a second fin;

the source/drain feature is a merged source/drain feature wrapping around the first fin and the second fin and having a concave top;

the silicide layer is disposed on the concave top; and

the metal layer is disposed on and contacting the seed metal layer.

5. The semiconductor device of claim 4 , wherein the source/drain feature is curved, defining a groove with a concave bottom surface, and wherein the seed metal layer fills in the groove and has a flat bottom surface.

6. The semiconductor device of claim 5 , wherein the flat bottom surface of the metal seed layer contacts a shallow trench isolation feature.

7. The semiconductor device of claim 4 , wherein a lowermost point of the concave top is below a topmost surface of the source/drain feature and above a topmost point of the fin.

8. A semiconductor device, comprising:

a fin disposed on a substrate;

a source/drain feature disposed around a top portion of the fin;

a silicide layer wrapping around the source/drain feature;

a seed metal layer over the silicide layer; and

a metal plug disposed over and contacting the seed metal layer,

wherein the seed metal layer is in direct contact with a bottom surface of the metal plug and in direct contact with the silicide layer, and is free of contact with sidewalls of the metal plug.

9. The semiconductor device of claim 8 , wherein the seed metal layer wraps around the silicide layer.

10. The semiconductor device of claim 9 , further comprising a spacer over sidewalls of the metal plug, wherein the spacer lands on a top surface of the seed metal layer.

11. The semiconductor device of claim 8 , wherein

the fin is a first fin and the source/drain feature is a first source/drain feature;

the semiconductor device further includes a second fin and a second source/drain feature wrapping around the second fin;

the first source/drain feature and the second source/drain feature are merged together, defining a groove over a shared surface;

the silicide layer wraps around the first source/drain feature and the second source/drain feature; and

the metal plug lands over the groove.

12. The semiconductor device of claim 11 , wherein the seed metal layer is disposed over the groove and interposed between the silicide layer and the metal contact, and wherein the seed metal layer includes a metal different than that included in the metal contact.

13. A semiconductor device, comprising:

a fin disposed on a substrate;

a source/drain feature wrapping around a top portion of the fin;

a silicide layer wrapping around the source/drain feature;

a seed metal layer wrapping around the silicide layer; and

a metal plug formed directly on the seed metal layer; and

a dielectric spacer disposed on and in direct contact with sidewalls of the metal plug.

14. The semiconductor device of claim 13 , wherein a portion of the seed metal layer is below an uppermost surface of the fin.

15. The semiconductor device of claim 13 , wherein a total thickness of the silicide layer and the metal plug is at least three times of a width of the metal plug, the width being in a direction along which the fin runs.

16. The semiconductor device of claim 13 , wherein the fin is a first fin, and wherein the semiconductor device further comprising:

a second fin adjacent to the first fin;

the source/drain feature being a joint source/drain feature wrapping around the first fin and the second fin with a groove at a top surface of the joint source/drain feature;

the silicide layer wrapping around the joint source/drain feature, thereby lining the groove; and

the metal plug landing on and contacting the seed metal layer in the groove.

17. The semiconductor device of claim 16 , wherein the dielectric spacer is disposed over a top surface of the seed metal layer.

18. The semiconductor device of claim 16 , wherein

the groove is a first groove;

the joint source/drain feature defines a second groove at a bottom surface of the joint source/drain feature;

the silicide layer contours the source/drain feature in the groove; and

the metal seed layer is disposed over the silicide layer and fills the groove.

19. The semiconductor device of claim 13 , further comprising an over-burden metal layer over the metal plug, wherein the over-burden metal layer has a first width and a second width at a top portion and a bottom portion of the over-burden metal layer, respectively, wherein the metal plug has a third width, and wherein the first width is greater than the second width and the second width is greater than the first width.

20. The semiconductor device of claim 19 , further comprising a spacer layer over sidewalls of the bottom portion of the over-burden metal layer.