Strained nanowire CMOS device and method of forming

1. A semiconductor device comprising:

a substrate;

first source/drain regions and a first channel region interposed between the first source/drain regions, the first source/drain regions and the first channel region comprising alternating layers of first epitaxial layers and second epitaxial layers, the first epitaxial layers and the second epitaxial layers extending continuously between the first source/drain regions;

second source/drain regions and a second channel region interposed between the second source/drain regions, the second source/drain regions comprising alternating layers of the first epitaxial layers and the second epitaxial layers, the second channel region comprising the second epitaxial layers wherein a gap in the first epitaxial layers exists between the second source/drain regions;

a first gate electrode extending over the first channel region; and

a second gate electrode extending over the second channel region.

2. The semiconductor device of claim 1 , wherein a width of the second epitaxial layers in the first channel region is less than a width of the first epitaxial layers in the first channel region in a direction perpendicular to current flow through the first channel region.

3. The semiconductor device of claim 1 , wherein edges of the second epitaxial layers in the second channel region are rounded in a direction perpendicular to current flow through the second channel region.

4. The semiconductor device of claim 1 , wherein the first source/drain regions comprise a third epitaxial layer extending along sidewalls of the first epitaxial layers and the second epitaxial layers.

5. The semiconductor device of claim 4 , wherein the second source/drain regions comprise a fourth epitaxial layer extending along sidewalls of the first epitaxial layers and the second epitaxial layers, wherein the third epitaxial layer and the fourth epitaxial layer are formed of different materials.

6. The semiconductor device of claim 1 , further comprising a first gate dielectric over the second channel region, the first gate dielectric extending between adjacent ones of the second epitaxial layers in the second channel region.

7. The semiconductor device of claim 1 , wherein the first gate electrode and the second gate electrode is a same continuous gate electrode.

8. A semiconductor device comprising:

a substrate;

first source/drain regions and a first channel region interposed between the first source/drain regions, the first source/drain regions and the first channel region comprising alternating layers of first epitaxial layers and second epitaxial layers, the first epitaxial layers in the first channel region having a greater width than the second epitaxial layers in the first channel region in a direction perpendicular to current flow through the first channel region;

second source/drain regions and a second channel region interposed between the second source/drain regions, the second source/drain regions and the second channel region comprising alternating layers of the first epitaxial layers and the second epitaxial layers, the second epitaxial layers in the second channel region having a greater width than the first epitaxial layers in the second channel region in a direction perpendicular to current flow through the second channel region; and

a gate electrode extending over the first epitaxial layers and the second epitaxial layers in the first channel region and the second channel region.

9. The semiconductor device of claim 8 , wherein a bottommost layer of the first epitaxial layers in the second channel region is removed.

10. The semiconductor device of claim 8 , further comprising a gate dielectric interposed between the gate electrode and the second channel region, wherein the gate dielectric extends between a bottommost second epitaxial layer in the second channel region and the substrate.

11. The semiconductor device of claim 8 , wherein sidewalls of the second epitaxial layers in the first channel region are concave in a direction perpendicular to current flow through the first channel region.

12. The semiconductor device of claim 11 , wherein sidewalls of the first epitaxial layers in the second channel region are concave in a direction perpendicular to current flow through the second channel region.

13. The semiconductor device of claim 8 , wherein the first channel region has one less second epitaxial layer than the second channel region.

14. The semiconductor device of claim 8 , further comprising a dielectric layer over the substrate, the dielectric layer having a first thickness adjacent the first channel region and a second thickness adjacent the second channel region, the first thickness being different than the second thickness.

15. A semiconductor device comprising:

a substrate;

a first transistor comprising a first channel region and a first gate electrode, the first channel region comprising alternating layers of a first epitaxial material and a second epitaxial material, wherein sidewalls of the first epitaxial material in the first channel region have a first shape, wherein the first gate electrode overlies the alternating layers of the first epitaxial material and the second epitaxial material in the first channel region; and

a second transistor comprising a second channel region and a second gate electrode, the second channel region comprising alternating layers of the first epitaxial material and the second epitaxial material, wherein the second gate electrode overlies the alternating layers of the first epitaxial material and the second epitaxial material in the second channel region, wherein sidewalls of the first epitaxial material in the second channel region has a second shape different than the first shape.

16. The semiconductor device of claim 15 , wherein the first shape is concave.

17. The semiconductor device of claim 16 , wherein the second shape is linear.

18. The semiconductor device of claim 15 , wherein the first shape is a “V” shape.

19. The semiconductor device of claim 15 , wherein the first transistor comprises a first gate dielectric, the first gate dielectric extending from a first sidewall of a bottommost second epitaxial material between the bottommost second epitaxial material and the substrate to a second sidewall of the bottommost second epitaxial material in a direction perpendicular to current flow in the first channel region.

20. The semiconductor device of claim 15 , wherein the second transistor has more layers of the second epitaxial material in the second channel region than in the first channel region.