Epitaxial features confined by dielectric fins and spacers

1. A semiconductor structure, comprising:

a first semiconductor fin extending upwardly from a semiconductor substrate;

an isolation structure over the semiconductor substrate and on sidewalls of the first semiconductor fin;

a first epitaxial feature over the first semiconductor fin;

a dielectric fin partially embedded in the isolation structure and projecting upwardly above the isolation structure, wherein a portion of the isolation structure is disposed between the dielectric fin and the semiconductor substrate thereby preventing the dielectric fin from interfacing with the semiconductor substrate; and

first and second spacer features over the isolation structure, wherein the first spacer feature is laterally between the first epitaxial feature and the dielectric fin, and the first epitaxial feature is laterally between the first and second spacer features.

2. The semiconductor structure of claim 1 , wherein the first epitaxial feature is in direct contact with both the first and second spacer features.

3. The semiconductor structure of claim 2 , further comprising an oxide layer between the first spacer feature and the dielectric fin.

4. The semiconductor structure of claim 1 , further comprising a second semiconductor fin extending upwardly from the semiconductor substrate and through the isolation structure, wherein the dielectric fin is positioned laterally between the first and second semiconductor fins.

5. The semiconductor structure of claim 4 , further comprising:

a second epitaxial feature over the second semiconductor fin; and

third and fourth spacer features over the isolation structure, wherein the third spacer feature is laterally between the second epitaxial feature and the dielectric fin, and the second epitaxial feature is laterally between the third and fourth spacer features.

6. The semiconductor structure of claim 1 , further comprising a conductive feature over and in direct contact with the first epitaxial feature, wherein the conductive feature is also disposed over a top surface and sidewall surfaces of the dielectric fin.

7. The semiconductor structure of claim 1 , wherein a first width of the first epitaxial feature as measured across top surfaces of the first and second spacer features is greater than a second width of the first epitaxial feature as measured at half-height of the first epitaxial feature.

8. The semiconductor structure of claim 1 , further comprising a gate stack over and engaging the first semiconductor fin and the dielectric fin, wherein a first height of the dielectric fin directly under the gate stack is greater than a second height of the dielectric fin adjacent to but not directly under the gate stack.

9. The semiconductor structure of claim 1 , wherein:

the dielectric fin includes one of silicon carbide nitride, silicon oxycarbide, and silicon oxycarbide nitride; and

each of the first and second spacer features includes one of silicon carbide nitride, silicon oxycarbide, and silicon oxycarbide nitride.

10. The semiconductor structure of claim 1 , wherein the dielectric fin includes a metal oxide.

11. A semiconductor structure, comprising:

a substrate;

first and second semiconductor fins extending upwardly from the substrate, wherein the first semiconductor fin extends to a first height over the substrate;

an isolation structure over the substrate and on sidewalls of the first and second semiconductor fins;

first and second epitaxial features over the first and second semiconductor fins respectively;

a dielectric fin partially embedded in the isolation structure and projecting upwardly above the isolation structure, wherein the dielectric fin is between the first and second semiconductor fins, wherein the dielectric fin and the first and second semiconductor fins are arranged lengthwise along a same direction from a top view, wherein the dielectric fin extends to a second height over the substrate that is greater than the first height; and

first and second spacer features over the isolation structure, wherein the first spacer feature is laterally between the first epitaxial feature and the dielectric fin, and the second spacer feature is laterally between the dielectric fin and the second epitaxial feature, wherein a majority of the first and second epitaxial features are below a top surface of the first and second spacer features.

12. The semiconductor structure of claim 11 , wherein a ratio between a width of the first epitaxial feature to a width of the first semiconductor fin is in a range from about 1.0 to about 1.5.

13. The semiconductor structure of claim 11 , further comprising:

a conductive feature over and in direct contact with the dielectric fin, the first and second spacer features, and the first and second epitaxial features, wherein the conductive feature wraps around a top portion of the dielectric fin.

14. The semiconductor structure of claim 11 , further comprising third and fourth spacer features over the isolation structure, wherein the first epitaxial feature is in direct contact with the first and third spacer features on both sides of the first epitaxial feature, and the second epitaxial feature is in direct contact with the second and fourth spacer features on both sides of the second epitaxial feature.

15. The semiconductor structure of claim 11 , further comprising an oxide layer between the dielectric fin and each of the first and second spacer features.

16. A semiconductor structure, comprising:

a substrate;

a semiconductor fin extending upwardly from the substrate;

an epitaxial feature over the semiconductor fin;

an isolation structure over the substrate and on sidewalls of the semiconductor fin;

first and second dielectric fins partially embedded in the isolation structure and projecting upwardly above the isolation structure, wherein the semiconductor fin is between the first and second dielectric fins;

a gate stack over and engaging the semiconductor fin and the first and second dielectric fins;

a spacer layer covering sidewalls of the gate stack and sidewalls of each of the first and second dielectric fins, wherein the spacer layer also covers sidewalls of the epitaxial feature; and

a contact disposed over the first dielectric fin, wherein the first dielectric fin extends into the contact.

17. The semiconductor structure of claim 16 , wherein a portion of the spacer layer is laterally between the first dielectric fin and the epitaxial feature.

18. The semiconductor structure of claim 16 , wherein a top surface of the first dielectric fin is above a top surface of the epitaxial feature.

19. The semiconductor structure of claim 16 , wherein in a region adjacent to but not directly under the gate stack, a top surface of the first dielectric fin is above a top surface of the second dielectric fin.

20. The semiconductor structure of claim 16 , further comprising:

a conductive feature over and in direct contact with the epitaxial feature; and

an interlayer dielectric layer over and in direct contact with the first and second dielectric fins, wherein a portion of the interlayer dielectric layer is vertically between the conductive feature and the first dielectric fin.