Methods of fabricating semiconductor structures having epitaxially grown source and drain elements
Methods for fabricating facetless semiconductor structures using commercially available chemical vapor deposition systems are disclosed herein. A key aspect of the invention includes selectively depositing an epitaxial layer of at least one semiconductor material on the semiconductor substrate while in situ doping the epitaxial layer to suppress facet formation. Suppression of faceting during selective epitaxial growth by in situ doping of the epitaxial layer at a predetermined level rather than by manipulating spacer composition and geometry alleviates the stringent requirements on the device design and increases tolerance to variability during the spacer fabrication.
1. A method of fabricating a semiconductor structure, the method comprising:
providing a semiconductor substrate;
forming a gate stack over a first portion of the semiconductor substrate, the gate stack comprising a dielectric and defining a channel therebelow; and
selectively depositing an epitaxial layer comprising at least one semiconductor material proximate the gate stack while in situ doping the epitaxial layer to a first predetermined level, to thereby suppress formation of facets on the epitaxial layer, wherein an ambient pressure during selective deposition of the epitaxial layer is greater than about 5 Torr and the channel is strained.
2. The method of claim 1 , wherein depositing the epitaxial layer comprises defining at least one of a source element and a drain element proximate the gate stack.
3. The method of claim 1 , wherein the selective deposition of the epitaxial layer results in the formation of a substantially facetless semiconductor region.
4. The method of claim 1 , wherein the epitaxial layer is deposited in a single-wafer reduced-pressure chemical vapor deposition system.
5. The method of claim 1 , wherein the dielectric comprises a two-layered spacer structure comprising a silicon oxide liner and a silicon nitride spacer disposed thereon.
6. The method of claim 5 , wherein the silicon oxide liner undercuts the silicon nitride spacer such that the silicon nitride spacer extends further laterally from the gate stack than the silicon oxide liner.
7. The method of claim 1 , further comprising forming a contact material above the epitaxial layer, wherein the contact material comprises at least one material selected from the group consisting of nickel and tungsten.
8. The method of claim 7 , wherein the contact material comprises nickel.
9. The method of claim 7 , wherein the contact material comprises tungsten.
10. The method of claim 1 , wherein the strained channel consists essentially of silicon.
11. The method of claim 10 , wherein the epitaxial layer comprises silicon and germanium.
12. The method of claim 11 , wherein the step of selectively depositing an epitaxial layer comprises use of at least one precursor gas, the at least one precursor gas comprising dichlorosilane and germane.
13. The method of claim 12 , wherein the ambient pressure is less than approximately 20 Torr.
14. The method of claim 12 , wherein an ambient temperature during the selective deposition of the epitaxial layer is selected from a range of 500° C. to about 900° C.
15. The method of claim 14 , wherein the ambient temperature is approximately 750° C.
16. The method of claim 14 , wherein the ambient temperature is approximately 700° C.
17. The method of claim 12 , wherein the epitaxial layer extends to a height above the substrate ranging from about 10 nm to about 100 nm.
18. The method of claim 12 , wherein the substrate comprises an insulating layer.
19. The method of claim 12 , wherein the step of selectively depositing an epitaxial layer comprises use of a carrier gas, and the carrier gas comprises hydrogen.
20. The method of claim 19 , wherein the carrier gas consists essentially of hydrogen.
21. The method of claim 12 , wherein the step of selectively depositing an epitaxial layer comprises use of an etchant, and the etchant comprises at least one of hydrogen chloride and chlorine.
22. The method of claim 21 , wherein the etchant comprises hydrogen chloride.
23. The method of claim 22 , wherein the step of selectively depositing an epitaxial layer comprises use of a carrier gas, and the carrier gas consists essentially of hydrogen.