Semiconductor device and method

1. A method comprising:

depositing a first dummy gate over and along sidewalls of a first fin extending upwards from a substrate;

forming a first gate spacer along a sidewall of the first dummy gate;

forming a first recess in the first fin adjacent the first gate spacer; and

forming a first source/drain region in the first recess, the forming the first source/drain region comprising:

epitaxially growing a first layer in the first recess, the first layer comprising silicon and carbon;

epitaxially growing a second layer on the first layer, the second layer having a different material composition than the first layer, the first layer separating the second layer from the first fin; and

epitaxially growing a third layer on the second layer, the third layer having a different material composition than the first layer.

2. The method of claim 1 , wherein forming the first recess comprises:

performing an anisotropic etch process on the first fin, wherein after the anisotropic etch process, the first recess does not extend under the first gate spacer.

3. The method of claim 1 , wherein forming the first recess comprises:

performing an anisotropic etch process on the first fin; and

after the anisotropic etch process, performing an isotropic etch process on the first fin, wherein after the isotropic etch process, the first recess extends under the first gate spacer.

4. The method of claim 1 further comprising:

replacing the first dummy gate with a functional gate stack disposed over and along sidewalls of the first fin.

5. The method of claim 1 further comprising:

forming a lightly-doped drain region at an upper surface of the first fin, wherein the first recess extends through the lightly-doped drain region, and wherein the first layer extends along the lightly-doped drain region.

6. The method of claim 1 , wherein the first layer has a uniform thickness at sides and a bottom of the first recess.

7. The method of claim 1 , wherein the first layer is thicker at a bottom than at sides of the first recess.

8. The method of claim 1 , wherein the second layer has a faceted top surface raised above an upper surface of the first fin, and wherein the third layer has a uniform thickness on the faceted top surface of the second layer.

9. A method comprising:

forming a first dummy gate over and along sidewalls of a first fin extending upwards from a substrate;

forming a first gate spacer along a sidewall of the first dummy gate;

anisotropically etching a first recess in the first fin adjacent the first gate spacer;

epitaxially growing a first source/drain region in the first recess, the first source/drain region comprising a first epitaxial carbon-containing layer, a second epitaxial layer, and a third epitaxial layer, the first epitaxial carbon-containing layer lining the first recess, the second epitaxial layer being on the first epitaxial carbon-containing layer, the second epitaxial layer having a different material composition than the first epitaxial carbon-containing layer, and the third epitaxial layer being on the second epitaxial layer, the third epitaxial layer having a different material composition than the first epitaxial carbon-containing layer; and

replacing the first dummy gate with a functional gate stack disposed over and along sidewalls of the first fin.

10. The method of claim 9 further comprising:

after anisotropically etching the first recess, performing an isotropic etch process on the first recess, wherein after the isotropic etch process, the first recess extends under the first gate spacer.

11. The method of claim 9 , wherein the first epitaxial carbon-containing layer of the first source/drain region prevents material of the functional gate stack from extending into the first source/drain region.

12. The method of claim 9 , wherein the first epitaxial carbon-containing layer is thicker at a bottom than at sides of the first recess.

13. A method comprising:

forming a first gate over and along sidewalls of a first fin, the first fin extending from a substrate;

forming a first gate spacer along a sidewall of the first gate;

etching a first recess in the first fin adjacent the first gate spacer; and

epitaxially growing a first layer in the first recess, the first layer comprising silicon and carbon;

epitaxially growing a second layer on the first layer, the second layer having a faceted top surface, the second layer having a different material composition than the first layer, the first layer completely separating the second layer from the first fin; and

epitaxially growing a third layer on the second layer, the third layer having a uniform thickness on the faceted top surface of the second layer, the third layer having a different material composition than the first layer.

14. The method of claim 13 , wherein the first layer has a uniform thickness at sides and a bottom of the first recess.

15. The method of claim 13 , wherein the first layer is thicker at a bottom of the first recess than at sides of the first recess.

16. The method of claim 13 , wherein the first layer has an atomic concentration of carbon in a range from 0.2% to 5%.

17. The method of claim 13 , wherein the third layer contacts the first layer and the first gate spacer.

18. The method of claim 13 further comprising:

after epitaxially growing the third layer, replacing the first gate with a second gate disposed over and along sidewalls of the first fin.

19. The method of claim 13 , wherein etching the first recess comprises:

performing an anisotropic etch process on the first fin; and

after the anisotropic etch process, performing an isotropic etch process on the first fin, wherein after the isotropic etch process, the first recess extends under the first gate spacer.

20. The method of claim 13 , wherein the first layer extends under the first gate spacer.