Method of forming extremely thin semiconductor on insulator (ETSOI) device without ion implantation

1. A method of fabricating a semiconductor device comprising:

providing a substrate comprising at least a first semiconductor layer atop a dielectric layer,

wherein the first semiconductor layer has a thickness of less than 10 nm;

forming a gate structure directly on the first semiconductor layer;

forming a spacer on the gate structure,

forming an in-situ doped semiconductor material on the first semiconductor layer adjacent to the spacer on the gate structure, wherein the in-situ doped semiconductor material is in direct contact with an interface between a base of the spacer and the first semiconductor layer and the in-situ doped semiconductor material is not in contact with a sidewall of the spacer; and

diffusing dopant from the in-situ doped semiconductor material into the first semiconductor layer to form extension regions.

2. The method of claim 1 , wherein the substrate further comprises a second semiconductor layer separated from the first semiconductor layer by the dielectric layer.

3. The method of claim 1 , wherein the first semiconductor layer has a thickness ranging from 1.0 nm to 5.0 nm.

4. The method of claim 1 , wherein the forming of the in-situ doped semiconductor material comprises epitaxial growth of p-type doped SiGe.

5. The method of claim 4 , wherein the p-type doped SiGe comprise a dopant concentration ranging from 1×10 19 atoms/cm 3 to 2×10 21 atoms/cm 3 .

6. The method of claim 5 , wherein a p-type dopant of the p-type doped SiGe comprises boron, aluminum, gallium or indium.

7. The method of claim 1 , wherein the forming of the in-situ doped semiconductor material on the first semiconductor layer comprises epitaxial growth of n-type doped Si:C.

8. The method of claim 7 , wherein the n-type doped Si:C comprises a dopant concentration ranging from 1×10 19 atoms/cm 3 to 2×10 21 atoms/cm 3 .

9. The method of claim 8 , wherein a n-type dopant of the n-type doped Si:C comprises antimony, arsenic or phosphorous.

10. The method of claim 1 , wherein the diffusing dopant from the in-situ doped semiconductor material into the first semiconductor layer comprises annealing.

11. The method of claim 10 , wherein the annealing comprises rapid thermal annealing, furnace annealing, flash lamp annealing or laser annealing.

12. The method of claim 1 , wherein the in-situ doped semiconductor material provides raised source and drain regions.

13. A planar semiconductor device comprising:

a substrate having a layer of semiconductor material atop an insulating layer, wherein the layer of semiconductor material has at thickness of less than 10.0 nm;

a gate structure present on the layer of the semiconductor material;

a spacer on the gate structure,

doped epitaxial raised source and drain regions present atop the layer of semiconductor material on opposing sides of the gate structure, the doped epitaxial raised source and drain regions are in direct contact with an interface between a base of the spacer and the layer of semiconductor material, and the doped epitaxial raised source and drain regions are not in contact with a sidewall of the spacer; and

extension diffusions extending from the doped epitaxial raised source and drain regions into the layer of semiconductor material.