FET with wrap-around silicide and fabrication methods thereof

1. A semiconductor device, comprising:

a semiconductor fin disposed over a substrate;

an isolation structure at least partially surrounding the semiconductor fin;

a source/drain (S/D) feature disposed over the semiconductor fin, wherein an extended portion of the S/D feature extends over the isolation structure, the extended portion includes a first, a second, and a third epitaxial layer, the second epitaxial layer being embedded between the first and third epitaxial layers; and

a silicide layer disposed over the S/D feature, wherein the silicide layer wraps around the extended portion of the S/D feature such that the silicide layer is disposed along bottom and side surfaces of the first epitaxial layer.

2. The semiconductor device of claim 1 , wherein the first, second, and third epitaxial layers are doped, and the first epitaxial layer is more heavily doped than the second and third epitaxial layers.

3. The semiconductor device of claim 2 , wherein the third epitaxial layer has a greater amount of dopants than the second epitaxial layer.

4. The semiconductor device of claim 2 , wherein the silicide layer is further disposed along a top surface of the third epitaxial layer.

5. The semiconductor device of claim 1 , wherein the semiconductor device further comprises a spacer layer directly on a side portion and a bottom portion of the silicide layer.

6. The semiconductor device of claim 5 , further comprising a dielectric fin disposed over the substrate and adjacent to the semiconductor fin, wherein the spacer layer covers a top surface of the dielectric fin.

7. The semiconductor device of claim 5 , wherein the semiconductor device further comprises a gate structure disposed over a channel region of the semiconductor fin, wherein the spacer layer is disposed between a sidewall of the gate structure and the side portion of the silicide layer.

8. The semiconductor device of claim 7 , wherein the semiconductor device further comprises an interlayer dielectric (ILD) layer directly contacting the spacer layer.

9. A semiconductor device, comprising:

a semiconductor fin protruding from a substrate;

a shallow trench isolation (STI) structure adjacent a sidewall of the semiconductor fin;

an epitaxial source/drain (S/D) feature over the semiconductor fin, the epitaxial S/D feature having an extended portion directly above the STI structure;

a silicide layer over the epitaxial S/D feature, the silicide layer fully wrapping around the extended portion of the epitaxial S/D feature; and

a spacer layer wrapping around the silicide layer, wherein a portion of the spacer layer is disposed between the STI structure and the silicide layer.

10. The semiconductor device of claim 9 , wherein the spacer layer covers an upper tilted side surface and a lower tilted side surface of the silicide layer.

11. The semiconductor device of claim 9 , wherein the extended portion of the epitaxial S/D feature includes a first epitaxial layer and a second epitaxial layer, the second epitaxial layer is directly above the first epitaxial layer, and the first epitaxial layer has a greater amount of dopants than the second epitaxial layer.

12. The semiconductor device of claim 11 , wherein the silicide layer covers side and bottom surfaces of the first epitaxial layer, and the silicide layer covers a top surface of the second epitaxial layer.

13. The semiconductor device of claim 9 , further comprising a gate structure over a channel region of the semiconductor fin, wherein the spacer layer is disposed between the gate structure and a side surface of the silicide layer.

14. The semiconductor device of claim 9 , further comprising:

an interlayer dielectric (ILD) layer over the epitaxial S/D feature; and

an S/D contact penetrating through the ILD layer and penetrating through a top portion of the spacer layer to contact a top surface of the silicide layer.

15. The semiconductor device of claim 9 , wherein the sidewall of the semiconductor fin is lined with a fin spacer layer, and the fin spacer layer is in direct contact with the STI structure.

16. The semiconductor device of claim 9 , further comprising a dielectric fin over the substrate, the dielectric fin in direct contact with side and bottom surfaces of the STI structure.

17. A semiconductor device, comprising:

a first and a second semiconductor fin protruding from a substrate;

an isolation feature over the substrate and over side surfaces of the first and second semiconductor fins;

a first and a second source/drain (S/D) feature over each of the respective first and second semiconductor fins, wherein the first and second S/D features have extended portions that extend directly above the isolation feature; and

a first and a second silicide layer over each of the respective first and second S/D features, wherein each of the first and second silicide layers fully wraps around the extended portions of each of the first and second S/D features,

wherein each of the extended portions of the first and second S/D features includes a plurality of epitaxial layers having different dopant concentrations.

18. The semiconductor device of claim 17 , further comprising a spacer layer in direct contact with each of the first and second silicide layers, the spacer layer being disposed over side surfaces of the first and second silicide layers.

19. The semiconductor device of claim 18 , further comprising:

a dielectric fin over the isolation feature and disposed between the first and second semiconductor fins; and

an interlayer dielectric (ILD) layer over the dielectric fin, wherein the spacer layer separates the dielectric fin from the ILD layer.

20. The semiconductor device of claim 18 , further comprising a first gate structure over a channel region of the first semiconductor fin, wherein the spacer layer is disposed between the first gate structure and the first silicide layer along a lengthwise direction of the first semiconductor fin.