Source/drain features with an etch stop layer

1. A semiconductor device, comprising:

a substrate having a first device region and a second device region;

a first fin extending from the substrate in the first device region and a second fin extending from the substrate in the second device region, wherein the first fin includes a first channel region and a first source/drain region and the second fin includes a second channel region and a second source/drain region;

a first epitaxial feature over the first fin in the first source/drain region, wherein the first epitaxial feature is doped with a first dopant of a first conductivity;

a second epitaxial feature over the second fin in the second source/drain region, wherein the second epitaxial feature is doped with a second dopant of a second conductivity different from the first conductivity; and

a dielectric layer on the first and second epitaxial features, wherein the dielectric layer is doped with the first dopant, and wherein the dielectric layer has a profile conformal to a surface profile of the first and second epitaxial features.

2. The semiconductor device of claim 1 , wherein the first device region is a p-type field effect transistor (pFET) region and the second device region is a n-type FET (nFET) region.

3. The semiconductor device of claim 2 , wherein the first conductivity is p-type conductivity and the second conductivity is n-type conductivity.

4. The semiconductor device of claim 1 , wherein the dielectric layer comprises silicon nitride.

5. The semiconductor device of claim 4 , wherein the dielectric layer has a thickness of 2 to 10 nm.

6. The semiconductor device of claim 1 , wherein the first dopant is boron.

7. The semiconductor device of claim 1 , wherein the second dopant is phosphorous.

8. The semiconductor device of claim 1 , wherein the first epitaxial feature comprises silicon germanium (SiGe).

9. The semiconductor device of claim 1 , wherein the second epitaxial feature comprises silicon (Si).

10. A semiconductor device, comprising:

a substrate; and

an n-type field effect transistor (nFET) on the substrate, the nFET including:

a first fin on the substrate, the first fin including a channel region and a source/drain region;

a second fin on the substrate, the second fin including a channel region and a source/drain region;

a first gate disposed over the channel region of the first fin and the channel region of the second fin;

a first epitaxial feature disposed over and extending between the source/drain region of the first fin and the source/drain region of the second fin, wherein the first epitaxial feature is doped with an n-type dopant; and

a doped dielectric layer disposed directly on and adjacent to the first epitaxial feature and having a top surface, wherein the doped dielectric layer is doped with boron (B), and wherein a portion of the top surface of the doped dielectric layer is at a height lower than a top surface of the first fin.

11. The semiconductor device of claim 10 , wherein the doped dielectric layer comprises silicon nitride.

12. The semiconductor device of claim 10 , wherein the first epitaxial feature comprises silicon (Si) and phosphorous (P).

13. The semiconductor device of claim 10 further comprising:

a p-type FET (pFET) on the substrate, the pFET including:

a third fin on the substrate, the third fin including a channel region and a source/drain region;

a fourth fin on the substrate, the fourth fin including a channel region and a source/drain region;

a second gate disposed over the channel region of the third fin and the channel region of the fourth fin;

a second epitaxial feature disposed over and extending between the source/drain region of the third fin and the source/drain region of the fourth fin, wherein the second epitaxial feature is doped with boron; and

the doped dielectric layer disposed directly on the second epitaxial feature, wherein the doped dielectric layer is doped with B.

14. The semiconductor device of claim 13 , wherein the second epitaxial feature comprises silicon germanium (SiGe).

15. The semiconductor device of claim 13 , wherein the nFET is immediately adjacent to the pFET.

16. A semiconductor device, comprising:

a substrate;

a fin extending from the substrate;

a source/drain feature disposed on the fin;

a doped etch stop layer disposed on the source/drain feature; and

an interlayer dielectric disposed on the doped etch stop layer, wherein at least a portion of the interlayer dielectric is disposed between the doped etch stop layer and the substrate.

17. The semiconductor device of claim 16 , wherein each of the source/drain feature and the doped etch stop layer have a first type conductivity.

18. The semiconductor device of claim 16 , wherein the source/drain feature and the doped etch stop layer have different conductivity types.

19. The semiconductor device of claim 16 , wherein the fin is a first fin and the source/drain feature is a first source/drain feature, the semiconductor device further comprising:

a second fin extending from the substrate adjacent the first fin; and

a second source/drain feature disposed on the second fin and physically contacting the first source/drain feature, wherein the doped etch stop layer is further disposed on the second source/drain feature.

20. The semiconductor device of claim 16 further comprising an isolation feature disposed on the substrate such that the fin extends through the isolation feature, wherein the doped etch stop layer is further disposed on the isolation feature.