Semiconductor device and method

1. A device comprising:

an isolation region on a substrate;

a first fin extending above a top surface of the isolation region;

a gate structure on the first fin; and

an epitaxial source/drain region adjacent the gate structure, the epitaxial source/drain region having a first main portion and a first projecting portion, the first main portion disposed in the first fin, the first projecting portion disposed on a first sidewall of the first fin and beneath the top surface of the isolation region.

2. The device of claim 1 , wherein a height of the first main portion of the epitaxial source/drain region is from 30% to 80% of an overall height of the first fin.

3. The device of claim 1 , wherein a height of the first projecting portion of the epitaxial source/drain region is from 10% to 20% of an overall height of the epitaxial source/drain region.

4. The device of claim 1 , wherein the epitaxial source/drain region comprises:

a liner layer on the first fin, the liner layer comprising boron-doped silicon-germanium having a first germanium concentration and a first boron concentration;

a main layer on the liner layer, the main layer comprising boron-doped silicon-germanium having a second germanium concentration and a second boron concentration; and

a finishing layer on the main layer, the finishing layer comprising boron-doped silicon-germanium having a third germanium concentration and a third boron concentration, the third germanium concentration less than the second germanium concentration and greater than the first germanium concentration, the third boron concentration less than the second boron concentration and greater than the first boron concentration.

5. The device of claim 4 , wherein the liner layer extends beneath the top surface of the isolation region, and wherein the main layer and the finishing layer are disposed over the top surface of the isolation region.

6. The device of claim 4 , wherein the liner layer and the main layer extend beneath the top surface of the isolation region, and wherein the finishing layer is disposed over the top surface of the isolation region.

7. The device of claim 4 , wherein the liner layer, the main layer, and the finishing layer extend beneath the top surface of the isolation region.

8. The device of claim 1 further comprising:

a second fin extending above the top surface of the isolation region,

wherein the gate structure is on the second fin, and

wherein the epitaxial source/drain region further has a second main portion and a second projecting portion, the second main portion disposed in the second fin, the second projecting portion disposed on a second sidewall of the second fin and beneath the top surface of the isolation region, the first sidewall of the first fin and the second sidewall of the second fin facing away from one another.

9. A device comprising:

an isolation region on a substrate;

a first fin extending above a top surface of the isolation region, the first fin having a first inner sidewall and a first outer sidewall;

a second fin extending above the top surface of the isolation region, the second fin having a second inner sidewall and a second outer sidewall, the first inner sidewall and the second inner sidewall facing one another; and

an epitaxial source/drain region in the first fin and the second fin, the epitaxial source/drain region extending a first distance along the first inner sidewall and the second inner sidewall, the epitaxial source/drain region extending a second distance along the first outer sidewall and the second outer sidewall, the first distance less than the second distance.

10. The device of claim 9 further comprising:

a first fin spacer disposed on the first inner sidewall of the first fin; and

a second fin spacer disposed on the second inner sidewall of the second fin.

11. The device of claim 9 , wherein the epitaxial source/drain region extends beneath the top surface of the isolation region.

12. The device of claim 9 , wherein the epitaxial source/drain region has a convex top surface.

13. A method comprising:

depositing a spacer layer on fins, the fins extending from an isolation region;

patterning the spacer layer to form inner fin spacers and outer fin spacers, the inner fin spacers disposed on inner sidewalls of the fins, the outer fin spacers disposed on outer sidewalls of the fins;

patterning first source/drain recesses in the fins;

after patterning the first source/drain recesses, performing a plasma etching process to recess the inner fin spacers, remove the outer fin spacers, and form second source/drain recesses in the isolation region beneath the outer fin spacers; and

growing an epitaxial source/drain region in the first source/drain recesses and the second source/drain recesses.

14. The method of claim 13 , wherein the plasma etching process etches the outer fin spacers at a faster rate than the inner fin spacers.

15. The method of claim 14 , wherein the spacer layer is formed of silicon oxycarbonitride, and the plasma etching process is an anisotropic etch performed with CF 4 at bias voltage in a range of 300 volts to 500 volts.

16. The method of claim 13 , wherein a depth of the first source/drain recesses is from 30% to 80% of an overall height of the fins.

17. The method of claim 13 , wherein a depth of the second source/drain recesses is from 10% to 20% of an overall height of the epitaxial source/drain region.

18. The method of claim 13 , wherein growing the epitaxial source/drain region comprises growing a plurality of layers, each of the layers grown in the first source/drain recesses, a subset of the layers grown in the second source/drain recesses.

19. The method of claim 13 , wherein growing the epitaxial source/drain region comprises growing a plurality of layers, each of the layers grown in the first source/drain recesses, each of the layers grown in the second source/drain recesses.

20. The method of claim 13 , wherein portions of the epitaxial source/drain region between the fins are separated from the isolation region by the inner fin spacers.