Source/drain structure for semiconductor device
The present disclosure describes a semiconductor structure and a method for forming the same. The semiconductor structure can include a substrate, a fin structure over the substrate, a gate structure over the fin structure, an epitaxial region formed in the fin structure and adjacent to the gate structure. The epitaxial region can embed a plurality of clusters of dopants.
1. A method, comprising:
forming a doped epitaxial layer over a substrate;
forming a metallic layer on the doped epitaxial layer; and
decreasing a dopant solubility of the doped epitaxial layer to form dopant clusters in the epitaxial layer.
2. The method of claim 1 , wherein forming the doped epitaxial layer comprises epitaxially growing a silicon germanium layer.
3. The method of claim 2 , wherein forming the doped epitaxial layer further comprises epitaxially growing an other silicon germanium layer, wherein the other silicon germanium layer has a germanium concentration different from that of the silicon germanium layer.
4. The method of claim 1 , wherein forming the doped epitaxial layer comprises doping the doped epitaxial layer with dopants at a doping concentration between about 5×10 20 /cm 3 and about 6×10 21 /cm 3 .
5. The method of claim 1 , wherein forming the metallic layer comprises depositing titanium, cobalt, nickel, tungsten, or a combination thereof.
6. The method of claim 1 , further comprising removing an unreacted portion of the metallic layer.
7. The method of claim 1 , wherein decreasing the dopant solubility of the doped epitaxial layer comprises annealing the doped epitaxial layer between about 700° C. to about 1000° C.
8. The method of claim 1 , wherein decreasing the dopant solubility of the doped epitaxial layer comprises annealing the doped epitaxial layer between about 0.001 seconds to about 0.1 seconds.
9. A method, comprising:
forming a fin structure over a substrate:
forming an epitaxial layer on the fin structure, wherein the epitaxial layer comprises dopants:
depositing a metallic layer on the epitaxial layer; and
forming dopant clusters in the epitaxial layer, comprising:
forming a silicide layer between the metallic layer and the epitaxial layer; and
reducing a solid solubility of the dopants in the epitaxial layer.
10. The method of claim 9 , wherein forming the epitaxial layer comprises forming a silicon germanium layer having an atomic concentration of germanium gradually increasing along a direction vertical to the substrate.
11. The method of claim 9 , wherein forming the epitaxial layer comprises doping the epitaxial layer with a concentration of dopants increasing along a direction vertical to the substrate.
12. The method of claim 9 , wherein forming the epitaxial layer comprises gradually increasing a gas flow rate of a dopant precursor over a growth time.
13. The method of claim 9 , wherein forming the epitaxial layer comprises growing the epitaxial layer in a recess structure of the fin structure.
14. The method of claim 9 , wherein forming the dopant clusters further comprises annealing the epitaxial layer.
15. A semiconductor structure, comprising:
a fin structure on a substrate:
an epitaxial layer on the fin structure and doped with dopants;
a silicide layer on the epitaxial layer; and
a plurality of dopant clusters embedded in the epitaxial layer and adjacent to the silicide layer, wherein the plurality of dopant clusters have a concentration greater than a maximum doping concentration determined by a solid solubility limit of the dopants in the epitaxial layer.
16. The semiconductor structure of claim 15 , wherein the plurality of dopant clusters comprise boron.
17. The semiconductor structure of claim 15 , wherein an atomic percentage of the plurality of dopant clusters in the epitaxial layer is from about 1% to about 10%.
18. The semiconductor structure of claim 15 , wherein the plurality of dopant clusters are distributed in a cluster region having a thickness less than 10 nm.
19. The semiconductor structure of claim 15 , wherein the epitaxial layer comprises a silicon germanium layer having an atomic concentration of germanium gradually increasing along a direction vertical to the substrate.
20. The semiconductor structure of claim 15 , wherein the plurality of dopant clusters surrounds horizontal and vertical interfaces between the epitaxial layer and the silicide layer.