Source/drain regions of semiconductor device and method of forming the same
A device includes a first nanostructure over a semiconductor substrate; a second nanostructure over the first nanostructure; a gate structure surrounding the first nanostructure and the second nanostructure; a first epitaxial region in the semiconductor substrate adjacent the gate structure, wherein the first epitaxial region is a first doped semiconductor material; and a second epitaxial region over the first epitaxial region, wherein the second epitaxial region is adjacent the first nanostructure and the second nanostructure, wherein the second epitaxial region is a second doped semiconductor material that is different from the first doped semiconductor material. In an embodiment, the first doped semiconductor material has a smaller doping concentration than the second doped semiconductor material.
1. A device comprising:
a first nanostructure over a semiconductor substrate;
a second nanostructure over the first nanostructure;
a gate structure surrounding the first nanostructure and the second nanostructure;
a first epitaxial region in the semiconductor substrate adjacent the gate structure, wherein the first epitaxial region is a first doped semiconductor material, wherein the first nanostructure overhangs a portion of the first epitaxial region; and
a second epitaxial region over the first epitaxial region, wherein the second epitaxial region is adjacent the first nanostructure and the second nanostructure, wherein the second epitaxial region is a second doped semiconductor material that is different from the first doped semiconductor material.
2. The device of claim 1 , wherein the first doped semiconductor material has a smaller doping concentration than the second doped semiconductor material.
3. The device of claim 1 , wherein a top surface of the first epitaxial region extends above a top surface of the semiconductor substrate.
4. The device of claim 1 , wherein the first doped semiconductor material and the second doped semiconductor material are oppositely doped.
5. The device of claim 1 , wherein the second doped semiconductor material is doped with p-type impurities.
6. The device of claim 1 , wherein the first doped semiconductor material is silicon germanium having a first atomic fraction of germanium, and wherein the second doped semiconductor material is silicon germanium having a second atomic fraction of germanium that is greater than the first atomic fraction of germanium.
7. The device of claim 6 , wherein the first atomic fraction of germanium is less than 0.2.
8. The device of claim 1 further comprising sidewall epitaxial regions on sidewalls of the first nanostructure and the second nanostructure, wherein the sidewall epitaxial regions comprise the first doped semiconductor material.
9. A device comprising:
a semiconductor fin protruding from a substrate, the semiconductor fin comprising a first recess;
a first nanostructure over the semiconductor fin;
a gate structure surrounding the first nanostructure; and
a first source/drain region adjacent the first nanostructure, wherein the first source/drain region comprises:
a first epitaxial region in the first recess, wherein the first epitaxial region has a first doping concentration, wherein the first epitaxial region fills the first recess; and
a second epitaxial region on the first epitaxial region, wherein the second epitaxial region has a second doping concentration that is greater than the first doping concentration.
10. The device of claim 9 , wherein the first doping concentration is in the range of 1×10 17 atoms/cm 3 to 1×10 20 atoms/cm 3 .
11. The device of claim 9 , wherein a top surface of the first epitaxial region is at least 3 nm below a bottom surface of the first nanostructure.
12. The device of claim 9 , wherein the first epitaxial region comprises n-type dopants and the second epitaxial region comprises p-type dopants.
13. The device of claim 9 , wherein the first epitaxial region has a gradient doping profile.
14. The device of claim 9 , wherein the second epitaxial region physically contacts the first nanostructure.
15. The device of claim 9 , wherein the first nanostructure protrudes into the second epitaxial region.
16. A device comprising:
a set of nanostructures on a substrate, wherein each nanostructure of the set of nanostructures comprises a channel region;
a first epitaxial region in the substrate adjacent the set of nanostructures, wherein the first epitaxial region has a first composition;
second epitaxial regions on respective sidewalls of respective nanostructures, wherein the second epitaxial regions have the first composition;
a third epitaxial region on the first epitaxial region and on the second epitaxial regions, wherein the third epitaxial region has a second composition that is different than the first composition, wherein the first composition and the second composition are oppositely doped; and
a gate structure on the set of nanostructures, wherein the gate structure surrounds the channel region of each nanostructure of the set of nanostructures.
17. The device of claim 16 , wherein the first composition has a smaller doping concentration than the second composition.
18. The device of claim 16 , wherein the first composition comprises n-type dopants and the second composition comprises p-type dopants.
19. The device of claim 16 , wherein the second epitaxial regions have facets.
20. The device of claim 16 , wherein the first composition and the second composition comprise silicon germanium.