Methods of forming epitaxial source/drain features in semiconductor devices
A method includes forming an epitaxial source/drain (S/D) feature over a semiconductor layer, where the epitaxial S/D feature includes silicon (Si) and germanium (Ge), forming a trench to expose a portion of the epitaxial S/D feature, annealing the exposed portion of the epitaxial S/D feature, where the annealing forms at a top surface of the epitaxial S/D feature a first region having a first Ge concentration and a second region disposed below the first region having a second Ge concentration that is less than the first Ge concentration, oxidizing the first region, removing the oxidized first region, and forming an S/D contact in the trench over the second region.
1. A method, comprising:
forming an epitaxial source/drain (S/D) feature over a semiconductor layer, wherein the epitaxial S/D feature includes silicon (Si) and germanium (Ge);
forming a trench to expose a portion of the epitaxial S/D feature;
annealing the exposed portion of the epitaxial S/D feature, wherein the annealing forms over a top surface of the epitaxial S/D feature a first region having a first Ge concentration and a second region disposed below the first region having a second Ge concentration that is less than the first Ge concentration;
oxidizing the first region;
removing the oxidized first region; and
forming an S/D contact in the trench over the second region.
2. The method of claim 1 , wherein annealing the exposed portion of the epitaxial S/D feature includes performing a melting laser anneal process.
3. The method of claim 1 , oxidizing the first region includes:
depositing a dielectric layer in the trench;
removing portions of the dielectric layer to form spacers; and
performing a wet clean process to the spacers, wherein performing the wet clean process oxidizes the first region to form silicon oxide and germanium oxide.
4. The method of claim 3 , wherein performing the wet clean process removes the germanium oxide.
5. The method of claim 3 , wherein performing the wet clean process includes treating the epitaxial S/D feature with an oxidizing etchant.
6. The method of claim 1 , wherein removing the oxidized first region includes performing an anisotropic dry etching process.
7. The method of claim 6 , wherein performing the anisotropic dry etching process includes applying an etchant including a fluorine-containing gas, an argon-containing gas, or a combination thereof.
8. The method of claim 1 , further comprising, after removing the oxidized first region and before forming the S/D contact, forming a silicide layer in the trench.
9. A method, comprising:
forming an epitaxial source/drain (S/D) feature over semiconductor fins, wherein the epitaxial S/D feature includes silicon and germanium;
forming a recess in the epitaxial S/D feature, wherein forming the recess includes:
removing a portion of the epitaxial S/D feature to form a trench;
performing an annealing process to a top portion of the epitaxial S/D feature exposed in the trench;
after performing the annealing process, oxidizing the top portion of the epitaxial S/D feature; and
forming a silicide layer over the epitaxial S/D feature, wherein forming the silicide layer removes the oxidized top portion of the epitaxial S/D feature to form the recess; and
forming an S/D contact over the silicide layer.
10. The method of claim 9 , wherein forming the epitaxial S/D feature merges the semiconductor fins together.
11. The method of claim 9 , wherein forming the epitaxial S/D feature includes forming a first epitaxial layer over the semiconductor fins and forming a second epitaxial layer over the first epitaxial layer, wherein the second epitaxial layer includes a greater amount of germanium than the first epitaxial layer.
12. The method of claim 11 , wherein performing the annealing process includes heating the top portion of the second epitaxial layer to above its melting temperature.
13. The method of claim 9 , wherein performing the annealing process is implemented by a melting laser anneal process.
14. The method of claim 13 , wherein oxidizing the top portion of the epitaxial S/D feature includes selectively oxidizing the top portion of the epitaxial S/D feature relative to a bottom portion disposed below the top portion.
15. The method of claim 13 , wherein forming the silicide layer includes performing a pre-cleaning process to the epitaxial S/D feature, and wherein performing the pre-cleaning process selectively removes the top portion of the epitaxial S/D feature relative to a bottom portion disposed below the top portion.
16. The method of claim 9 , wherein oxidizing the portion of the epitaxial S/D feature includes applying ozone to the portion of the epitaxial S/D feature.
17. A method, comprising:
providing an epitaxial source/drain (S/D) feature over semiconductor fins, wherein the epitaxial S/D feature merges the semiconductor fins, and wherein the epitaxial S/D feature includes silicon germanium;
forming a silicide layer over the epitaxial S/D feature, wherein forming the silicide layer includes:
forming a trench in the epitaxial S/D feature;
performing a melting laser anneal (MLA) to a first region of the epitaxial S/D feature exposed in the trench;
oxidizing the first region of the epitaxial S/D feature; and
forming the silicide layer over a second region of the epitaxial S/D feature disposed below the first region, wherein forming the silicide layer removes the oxidized first region; and
forming an S/D contact over the silicide layer.
18. The method of claim 17 , wherein performing the MLA melts the first region of the epitaxial S/D feature.
19. The method of claim 17 , wherein oxidizing the first region of the epitaxial S/D feature includes applying an aqueous oxidizer.
20. The method of claim 17 , wherein removing the oxidized first region includes etching the oxidized first region with an etchant including a fluorine-containing gas, an argon-containing gas, or a combination thereof.