Conformal source and drain contacts for multi-gate field effect transistors

1. A method of forming a field effect transistor (FET), comprising:

providing a fin, wherein the fin includes a first semiconductor material and has a source region, a channel region, and a drain region for the FET;

forming a gate stack over the channel region;

trimming the fin to reduce a width of the fin in the source and drain regions;

forming a semiconductor film over the source and drain regions, wherein the semiconductor film includes a doped second semiconductor material and is substantially conformal to the fin; and

depositing a metal over the semiconductor film, wherein the metal is operable to electrically communicate with the source and drain regions.

2. The method of claim 1 , wherein the forming of the semiconductor film is by selectively growing the doped second semiconductor material substantially in the (100) and (110) crystal orientation.

3. The method of claim 1 , wherein the forming of the gate stack includes:

forming a dummy gate stack over the channel region before the forming of the semiconductor film; and

replacing the dummy gate stack with the gate stack after the forming of the semiconductor film.

4. The method of claim 3 , before the trimming of the fin, further comprising:

forming a gate spacer over sidewalls of the dummy gate stack and a fin spacer over sidewalls of the fin, wherein the gate spacer and the fin spacer are of the same dielectric material;

selectively modifying the gate spacer to have a different etch resistance than that of the fin spacer; and

selectively etching the fin spacer thereby exposing the sidewalls of the fin.

5. The method of claim 4 , wherein the trimming of the fin also reduces a height of the fin in the source and drain regions.

6. The method of claim 1 , before the depositing of the metal, further comprising:

performing metallization of the semiconductor film to form a metalized layer, wherein the metalized layer covers at least a portion of a top surface and a portion of sidewall surfaces of the semiconductor film.

7. The method of claim 1 , before the depositing of the metal, further comprising:

depositing a dielectric layer over the semiconductor film, wherein the metal is operable to electrically communicate with the source and drain regions through the dielectric layer and the semiconductor film.

8. A method of forming a field effect transistor (FET), comprising:

providing a fin, wherein the fin includes a first semiconductor material and has a source region, a channel region, and a drain region for the FET;

forming a dummy gate stack over the channel region;

forming a gate spacer over sidewalls of the dummy gate stack;

trimming the fin to reduce a width of the fin in the source and drain regions;

forming a semiconductor film over the source and drain regions, wherein the semiconductor film includes a doped second semiconductor material and is substantially conformal to the fin;

performing a replacement gate process thereby replacing the dummy gate stack with a metal gate;

forming contact holes to expose a portion of a top surface and a portion of two sidewall surfaces of the semiconductor film; and

depositing a metal in the contact holes.

9. The method of claim 8 , wherein the trimming of the fin results in the source and drain regions having a smaller width and a smaller height than the channel region.

10. The method of claim 8 , after the forming of the contact holes and before the depositing of the metal, further comprising:

performing metallization of the semiconductor film to form a metalized layer over the portion of the top surface and the portion of the two sidewall surfaces of the semiconductor film.

11. The method of claim 8 , after the forming of the contact holes and before the depositing of the metal, further comprising:

depositing a dielectric layer over the portion of the top surface and the portion of the two sidewall surfaces of the semiconductor film, wherein the metal is operable to electrically communicate with the source and drain regions through the dielectric layer and the semiconductor film.

12. A method, comprising:

providing a fin, wherein the fin includes a first semiconductor material and has a source region, a channel region, and a drain region for a transistor;

forming a first gate stack engaging the fin in the channel region;

forming a spacer over the first gate stack and the fin;

selectively etching the spacer on top and sidewalls of the fin; and

trimming the fin to reduce a width of the fin in the source and drain regions.

13. The method of claim 12 , further comprising:

forming a semiconductor film over the fin in the source and drain regions, wherein the semiconductor film includes a doped second semiconductor material; and

depositing a metal over the semiconductor film, wherein the metal is operable to electrically communicate with the source and drain regions.

14. The method of claim 13 , before the depositing of the metal, further comprising:

performing metallization of the semiconductor film to form a metalized layer, wherein the metalized layer covers at least a portion of a top surface and a portion of sidewall surfaces of the semiconductor film, wherein the metal is deposited over the metalized layer.

15. The method of claim 13 , before the depositing of the metal, further comprising:

depositing a dielectric layer over the semiconductor film, wherein the metal is deposited over the dielectric layer and the dielectric layer reduces Fermi-level pinning effects between the metal and the semiconductor film.

16. The method of claim 15 , wherein the dielectric layer includes titanium oxide or tantalum oxide and has a thickness of at most 1 nanometer.

17. The method of claim 12 , wherein the fin protrudes out of an isolation structure, and the selectively etching of the spacer on top and sidewalls of the fin leaves a portion of the spacer on a corner at an intersection of the fin and the isolation structure.

18. The method of claim 12 , wherein the trimming of the fin also reduces a height of the fin in the source and drain regions compared to another height of the fin in the channel region.

19. The method of claim 13 , wherein the forming of the semiconductor film is by selectively growing the doped second semiconductor material substantially in the (100) and (110) crystal orientation.

20. The method of claim 12 , further comprising, before the selectively etching of the spacer on top and sidewalls of the fin, selectively modifying the spacer such that it has a different etch selectivity over the first gate stack than over the fin.