P-type strained channel in a fin field effect transistor (FinFET) device

1. A semiconductor device, comprising:

a substrate having an n-doped well feature;

an epitaxial silicon germanium fin formed over the n-doped well feature, the epitaxial silicon germanium fin having a lower part and an upper part, wherein the lower part has a lower germanium content than the upper part;

a channel in the epitaxial silicon germanium fin; and

lightly doped source-drain regions formed from the epitaxial silicon germanium fin, the lightly doped source-drain regions extending into the epitaxial silicon germanium fin, the lightly doped source-drain regions comprising a diffusion region having a dopant concentration decreasing from an interface between epitaxial source/drain regions and the epitaxial silicon germanium fin toward the channel, the lightly doped source-drain regions comprising an upper doped region over the diffusion region, the upper doped region having a uniform dopant concentration.

2. The semiconductor device of claim 1 , wherein the upper part has a germanium content in a range from about 20% to about 40%.

3. The semiconductor device of claim 1 , wherein the lower part has a germanium content in a range from about 10 to about 30%.

4. The semiconductor device of claim 3 , wherein the lower part has a germanium content that increases from a bottom to a top of the lower part.

5. The semiconductor device of claim 4 , wherein the increasing germanium content in the lower part is gradual.

6. The semiconductor device of claim 4 , wherein the increasing germanium content in the lower part increases in one or more steps of 5% or more germanium content increases.

7. The semiconductor device of claim 1 , wherein a height thickness of the lower part is greater than a height thickness of the upper part.

8. A semiconductor device, comprising:

an epitaxial silicon germanium fin formed over a substrate, the epitaxial silicon germanium fin having a lower part and an upper part, wherein the lower part has a lower germanium content than the upper part;

a channel formed from the epitaxial silicon germanium fin;

a gate formed over the epitaxial silicon germanium fin;

a doped source-drain formed proximate the channel; and

a lightly-doped source-drain region interposed between the doped source-drain and the channel, the lightly doped source-drain region extending into the epitaxial silicon germanium fin, the doped source-drain comprising a diffusion region having a dopant concentration decreasing from an interface between the doped source-drain and the epitaxial silicon germanium fin toward the channel, the doped source-drain comprising an upper doped region over the diffusion region, the upper doped region having a uniform dopant concentration.

9. The semiconductor device of claim 8 , wherein the lightly doped source-drain region is formed in the lower part of the epitaxial silicon germanium fin by dopant diffusion from the doped source-drain.

10. The semiconductor device of claim 9 , wherein the lightly doped source-drain region is formed in the upper part of the epitaxial silicon germanium fin by dopant diffusion from the doped source-drain.

11. The semiconductor device of claim 10 , wherein the lightly doped source-drain region is formed in the upper part of a top of the epitaxial silicon germanium fin by implantation.

12. The semiconductor device of claim 8 , wherein a ratio of a height thickness of the lower part of the epitaxial silicon germanium fin to the upper part is in a range from 1:1 to about 10:1.

13. The semiconductor device of claim 8 , wherein the doped source-drain comprises a bottom layer with a germanium content in a range from about 30% to about 50% and a top layer with a germanium content in a range from about 50% to about 70%.

14. The semiconductor device of claim 8 , wherein the doped source-drain is doped with a dopant selected from the group consisting of boron and antimony.

15. The semiconductor device of claim 8 , wherein the doped source-drain comprises three or more layers.

16. The semiconductor device of claim 8 , wherein the doped source-drain comprises a first layer, a second layer over the first layer, and a third layer over the second layer, wherein a dopant concentration is greater in the third layer than the second layer and a dopant concentration in the second layer is greater than the first layer.

17. The semiconductor device of claim 8 , wherein the doped source-drain comprises a germanium content which increases from a bottom to a top of the doped source-drain.

18. A semiconductor device, comprising:

an epitaxial silicon germanium fin over a substrate, the epitaxial silicon germanium fin having a lower part and an upper part, wherein the lower part has a lower germanium content than the upper part;

an epitaxial silicon layer over the epitaxial silicon germanium fin;

a gate formed over the epitaxial silicon layer;

epitaxial source/drain regions along opposing sides of the gate and the epitaxial silicon layer, the epitaxial source/drain regions being doped with a p-type dopant; and

a lightly-doped drain region extending through the epitaxial silicon layer and into the epitaxial silicon germanium fin, the lightly-doped region comprising a diffusion region having a dopant concentration decreasing from an interface between the epitaxial source/drain regions and the epitaxial silicon germanium fin toward a channel region, the lightly-doped drain region comprising an upper doped region over the diffusion region, the upper doped region having a uniform dopant concentration.

19. The semiconductor device of claim 18 , wherein the lower part has a lower germanium content than the epitaxial source/drain regions.

20. The semiconductor device of claim 19 , wherein the upper part has a lower germanium content than the epitaxial source/drain regions.