FETS and methods of forming FETS

1. A method comprising:

forming a raised portion of a substrate;

forming fins on the raised portion of the substrate;

forming an isolation region surrounding the fins, a first portion of the isolation region being on a top surface of the raised portion of the substrate between adjacent fins;

forming a gate structure over the fins; and

forming source/drain regions on opposing sides of the gate structure, wherein forming the source/drain regions comprises:

epitaxially growing a first epitaxial layer on the fins adjacent the gate structure;

etching back the first epitaxial layer;

epitaxially growing a second epitaxial layer on the etched first epitaxial layer; and

etching back the second epitaxial layer, the etched second epitaxial layer having a non-faceted top surface and faceted side surfaces, each of the faceted side surfaces having a first facet, a second facet, and a third facet, the first facet and the third facet being non-parallel and non-perpendicular to a major surface of the substrate, the second facet being between the first facet and the third facet, the second facet being perpendicular to the major surface of the substrate, the etched first epitaxial layer and the etched second epitaxial layer forming source/drain regions.

2. The method of claim 1 further comprising an air gap separating at least one source/drain region from the first portion of the isolation region.

3. The method of claim 2 further comprising:

forming a gate seal spacer on sidewalls of the gate structure, a first portion of the gate seal spacer being between the first portion of the isolation region and the air gap.

4. The method of claim 1 , wherein the forming the source/drain regions further comprises:

recessing the fins outside of the gate structure to have top surfaces below a top surface of the isolation region; and

epitaxially growing the first epitaxial layer from the recessed fins on opposing sides of the gate structures.

5. The method of claim 1 , wherein the first epitaxial layer and the second epitaxial layer comprise silicon phosphorous (SiP).

6. The method of claim 1 , wherein the etching back the first epitaxial layer and etching back the second epitaxial layer are performed in an environment having a first temperature and at a first pressure, the first temperature being in a range from 650° C. to 800° C. and the first pressure being in a range from 1 torr to 50 torr.

7. The method of claim 1 , wherein the etching back the first epitaxial layer and etching back the second epitaxial layer comprises etching the first epitaxial layer and the second epitaxial layer with hydrochloric acid.

8. The method of claim 1 , wherein after epitaxially growing the first epitaxial layer on the fin adjacent the gate structure and before etching back the first epitaxial layer, a top surface of the first epitaxial layer has first facets, wherein the etching back the first epitaxial layer removes the first facets.

9. The method of claim 8 , wherein the first facets have ( 111 ) crystalline orientations.

10. The method of claim 1 , wherein after etching back the first epitaxial layer, a top surface of the etched first epitaxial layer is lower than the top surface of the fins in a fin area and in an area between adjacent fins.

11. The method of claim 10 , wherein after etching back the second epitaxial layer, the non-faceted top surface of the etched second epitaxial layer is higher than the top surface of the fins in the fin area and in the area between adjacent fins.

12. A method comprising:

forming a first fin over a substrate;

forming an isolation region surrounding the first fin;

forming a first gate structure over the first fin;

recessing the first fin outside of the first gate structure to have a top surface below a top surface of the isolation region;

forming a first source/drain region from the recessed first fin outside of the first gate structure, wherein forming the first source/drain region comprises:

epitaxially growing a first epitaxial layer from the recessed first fin adjacent the first gate structure;

etching back the first epitaxial layer with a first etch back process, the first etch back process including silane and hydrochloric acid;

epitaxially growing a second epitaxial layer on the etched first epitaxial layer; and

etching back the second epitaxial layer with a second etch back process, the second etch back process including silane and hydrochloric acid, the etched first epitaxial layer and the etched second epitaxial layer forming the first source/drain region;

forming a second fin over the substrate, the second fin being adjacent the first fin, the isolation region surrounding the second fin, the first gate structure being over the second fin;

recessing the second fin outside of the first gate structure to have a top surface below a top surface of the isolation region; and

epitaxially growing a second source/drain region from the recessed second fin outside of the first gate structure, the first source/drain region and the second source/drain region merge together to form a continuous source/drain region, the isolation region forming an air gap between a top surface of the isolation region and the continuous source/drain region.

13. The method of claim 12 further comprising:

forming a gate seal spacer on sidewalls of the first gate structure, a first portion of the gate seal spacer being on the isolation region, the first portion of the gate seal spacer having a top surface above a top surface of the recessed first fin.

14. The method of claim 12 further comprising:

forming a gate seal spacer on sidewalls of the first gate structure, a first portion of the gate seal spacer being on the isolation region, the first portion of the gate seal spacer being between the air gap and the isolation region.

15. The method of claim 12 , wherein the first epitaxial layer and the second epitaxial layer comprise silicon phosphorous (SiP).

16. A method comprising:

forming a first fin over a substrate;

forming an isolation region surrounding the first fin;

forming a gate structure over the first fin; and

forming source/drain regions on opposing sides of the gate structure, wherein forming the source/drain regions comprises:

epitaxially growing a first epitaxial layer on the first fin adjacent the gate structure;

etching back the first epitaxial layer;

epitaxially growing a second epitaxial layer on the etched first epitaxial layer; and

etching back the second epitaxial layer, the etched first epitaxial layer and the etched second epitaxial layer forming source/drain regions, an air gap between at least one source/drain region and a top surface of the isolation region.

17. The method of claim 16 further comprising:

forming a gate seal spacer on sidewalls of the gate structure, a first portion of the gate seal spacer being between the isolation region and the air gap.

18. The method of claim 16 , wherein the forming the source/drain regions further comprises:

recessing the first fin outside of the gate structure to have top surfaces below a top surface of the isolation region; and

epitaxially growing the first epitaxial layer from the recessed fins on opposing sides of the gate structures.

19. The method of claim 16 , wherein after epitaxially growing the first epitaxial layer on the first fin adjacent the gate structure and before etching back the first epitaxial layer, a top surface of the first epitaxial layer has first facets, wherein the etching back the first epitaxial layer removes the first facets, and wherein after etching back the second epitaxial layer, the etched second epitaxial layer has a non-faceted top surface.

20. The method of claim 16 , wherein the etching back the first epitaxial layer and etching back the second epitaxial layer comprises etching the first epitaxial layer and the second epitaxial layer with silane and hydrochloric acid.