FinFet with source/drain regions comprising an insulator layer

1. A device comprising:

a first fin extending from a substrate;

a first gate stack over and along sidewalls of the first fin;

a first gate spacer disposed along a sidewall of the first gate stack; and

a first source/drain region in the first fin and adjacent the first gate spacer, the first source/drain region comprising:

a first insulator layer on the first fin;

a first epitaxial layer on the first insulator layer; and

a second epitaxial layer contacting the first insulator layer and the first epitaxial layer.

2. The device of claim 1 , wherein the first insulator layer is thicker at a bottom than at sides of the first source/drain region.

3. The device of claim 1 further comprising:

an air gap between the first insulator layer and the first epitaxial layer.

4. The device of claim 3 , wherein the air gap has a planar bottom surface and a non-planar top surface.

5. The device of claim 1 , wherein the first epitaxial layer has a faceted top surface.

6. The device of claim 1 further comprising:

an etch stop layer over the first source/drain region and on a sidewall of the first gate spacer;

a first interlayer dielectric over the etch stop layer;

a second interlayer dielectric over the first interlayer dielectric; and

a first conductive contact extending through the first and second interlayer dielectrics and the etch stop layer, the first conductive contact being electrically coupled to the first source/drain region.

7. The device of claim 1 , wherein the first epitaxial layer contacts the first gate spacer.

8. The device of claim 1 , wherein the second epitaxial layer is between and contacting the first epitaxial layer and the first fin.

9. The device of claim 1 , wherein the first insulator layer comprises silicon oxide, silicon nitride, hafnium oxide, or a combination thereof.

10. A device comprising:

a fin extending from a substrate;

a first gate over and along sidewalls of a first fin;

gate spacers along sidewalls of the first gate;

a first source/drain region in the first fin adjacent a first one of the gate spacers, the first source/drain region comprising:

a first insulator layer;

a first semiconductor layer over the first insulator layer and on the fin;

a second semiconductor layer over the first insulator layer and the first semiconductor layer, the second semiconductor layer having a higher impurity concentration than the first semiconductor layer; and

a gap between the first insulator layer and the second semiconductor layer, the gap being completely surrounded by the first insulator layer and the second semiconductor layer.

11. The device of claim 10 , wherein the first semiconductor layer is a conformal layer, and wherein the second semiconductor layer is not a conformal layer.

12. The device of claim 10 , wherein the second semiconductor layer contacts the first one of the gate spacers.

13. The device of claim 10 , wherein the second semiconductor layer has a faceted top surface raised above an upper surface of the first fin.

14. The device of claim 10 , wherein the first insulator layer is thicker at a bottom than at sides of the first source/drain region.

15. The device of claim 10 , wherein the gap has a planar bottom surface and a non-planar top surface.

16. The device of claim 10 further comprising:

an etch stop layer over the first source/drain region and on a sidewall of the gate spacers;

a first interlayer dielectric over the etch stop layer;

a second interlayer dielectric over the first interlayer dielectric; and

a first conductive contact extending through the first and second interlayer dielectrics and the etch stop layer, the first conductive contact being electrically coupled to the first source/drain region.

17. The device of claim 10 , wherein the first insulator layer comprises silicon oxide, silicon nitride, hafnium oxide, or a combination thereof.

18. A device comprising:

a first fin extending upwards from a substrate;

a first gate over and along sidewalls of a first fin;

a first gate spacer along a sidewall of the first gate;

a first source/drain region in the first fin, the first source/drain region comprising:

a non-conformal insulator layer;

a first epitaxial layer over the non-conformal insulator layer and on the first fin; and

a second epitaxial layer on the first epitaxial layer, the first epitaxial layer being between and contacting the first epitaxial layer and the first fin, the second epitaxial layer contacting the non-conformal insulator layer.

19. The device of claim 18 , wherein the non-conformal insulator layer is thicker at a bottom than at sides of the first source/drain region.

20. The device of claim 18 further comprising:

an air gap between the non-conformal insulator layer and the second epitaxial layer.