Methods to fabricate MOSFET devices using selective deposition process

1. A method for forming a silicon-based material on a substrate having dielectric materials and source and drains regions thereon within a process chamber, comprising:

exposing the substrate to a first process gas comprising dichlorosilane, a germanium source, a first etchant and a carrier gas to deposit a first silicon-containing layer thereon, wherein the first silicon-containing layer is selectively deposited on the source and drain regions of the substrate while the first silicon-containing layer is etched away on the surface of the dielectric materials of the substrate; and then

exposing the substrate to a second process gas comprising silane and a second etchant to deposit a second silicon-containing layer selectively over the surface of the first silicon-containing layer on the substrate.

2. The method of claim 1 , wherein the first process gas comprises:

the dichlorosilane at a flow rate within a range from about 50 sccm to about 200 sccm;

germane at a flow rate within a range from about 0.5 sccm to about 5 sccm;

hydrogen chloride at a flow rate within a range from about 30 sccm to about 500 sccm; and

hydrogen at a flow rate within a range from about 10 slm to about 30 slm.

3. The method of claim 2 , wherein the process chamber is pressurized to a pressure within a range from about 1 Torr to about 10 Torr.

4. The method of claim 1 , wherein the first silicon-containing layer is a recessed layer and the second silicon-containing layer is an elevated layer within a source/drain feature.

5. The method of claim 2 , wherein the first silicon-containing layer comprises a graded germanium concentration.

6. The method of claim 2 , wherein the first and second process gases each comprise a dopant precursor independently selected from the group consisting of diborane, arsine, phosphine and derivatives thereof.

7. The method of claim 6 , wherein the first and second silicon-containing layers each have a boron concentration independently within a range from about 5×10 19 atoms/cm 3 to about 2×10 20 atoms/cm 3 .

8. The method of claim 6 , wherein the first and second silicon-containing layers each comprise independently a graded dopant concentration.

9. The method of claim 1 , wherein the second process gas comprises:

the silane at a flow rate within a range from about 50 sccm to about 200 sccm; and

hydrogen chloride at a flow rate within a range from about 30 sccm to about 500 sccm.

10. The method of claim 9 , wherein the second process gas comprises a second germanium source.

11. The method of claim 10 , wherein the second silicon-containing layer has a germanium concentration greater than the first silicon-containing layer.

12. The method of claim 6 , wherein the second silicon-containing layer has a dopant concentration greater than the first silicon-containing layer.

13. A method for forming a silicon-based material on a substrate having dielectric materials and source and drains regions thereon within a process chamber, comprising:

exposing the substrate to a first process gas comprising dichlorosilane, a germanium source, a carbon source, a first etchant and a carrier gas to deposit a first silicon-containing layer thereon, wherein the first silicon-containing layer is selectively deposited on the source and drain regions of the substrate while the first silicon-containing layer is etched away on the surface of the dielectric materials of the substrate; and then

exposing the substrate to a second process gas comprising silane and a second etchant to deposit a second silicon-containing layer selectively over the surface of the first silicon-containing layer on the substrate.

14. The method of claim 13 , wherein the first silicon-containing layer has interstitial sites within a crystalline lattice and contains about 3 at % or less of carbon within the interstitial sites.

15. The method of claim 14 , further comprising annealing the first silicon-containing layer to incorporate at least a portion of the carbon within substitutional sites of the crystalline lattice.

16. The method of claim 15 , wherein the carbon source is methylsilane.

17. The method of claim 14 , wherein the first silicon-containing layer has a boron concentration greater than 1×10 20 atoms/cm 3 .

18. The method of claim 17 , wherein the boron concentration is about 2×10 20 atoms/cm 3 or higher.

19. The method of claim 14 , wherein the second silicon-containing layer has a boron concentration greater than 1×10 20 atoms/cm 3 .

20. The method of claim 19 , wherein the boron concentration is about 2×10 20 atoms/cm 3 or higher.

21. A method for forming a silicon-based material on a substrate having dielectric materials and source and drains regions thereon within a process chamber, comprising:

exposing the substrate to a first process gas comprising dichlorosilane, a germanium source, a carbon source, a first etchant and a carrier gas to deposit a first silicon-containing layer containing interstitial sites within a crystalline lattice and about 3 at % or less of carbon within the interstitial sites, wherein the first silicon-containing layer is selectively deposited on the source and drain regions of the substrate while the first silicon-containing layer is etched away on the surface of the dielectric materials of the substrate;

exposing the substrate to a second process gas comprising silane and a second etchant to deposit a second silicon-containing layer selectively over the surface of the first silicon-containing layer on the substrate; and then

annealing the first silicon-containing layer to incorporate at least a portion of the carbon within substitutional sites of the crystalline lattice.