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:
providing a substrate;
forming a first epitaxial layer over the substrate, wherein forming the first epitaxial layer comprises doping the first epitaxial layer with a first dopant having a first concentration;
forming a second epitaxial layer over the first epitaxial layer, wherein forming the second epitaxial layer comprises doping the second epitaxial layer with a second dopant having a second concentration greater than the first concentration; and
precipitating the second dopant to form a cluster of the second dopant in the second epitaxial layer.
2. The method of claim 1 , wherein forming the first epitaxial layer comprises epitaxially growing a first silicon germanium layer with a first germanium concentration, and wherein forming the second epitaxial layer comprises epitaxially growing a second silicon germanium layer with a second germanium concentration greater than the first germanium concentration.
3. The method of claim 1 , wherein doping the first and the second epitaxial layers comprises flowing a precursor gas containing boron during a deposition process.
4. The method of claim 1 ,
wherein the second concentration is between about 5×10 20 /cm 3 and about 6×10 21 /cm 3 , and wherein precipitating the second dopant comprises forming a silicide layer in the second epitaxial layer.
5. The method of claim 4 , wherein forming the silicide layer comprises forming the silicide layer proximate to the first epitaxial layer, and wherein a separation between the silicide layer and the first epitaxial layer is less than about 5 nm.
6. The method of claim 1 , further comprising forming a third epitaxial layer over the second epitaxial layer, wherein forming the third epitaxial layer comprises doping the third epitaxial layer with a third dopant having a third concentration, less than the second concentration, in the third epitaxial layer.
7. The method of claim 1 , further comprising forming a third epitaxial layer over the second epitaxial layer, wherein forming the third epitaxial layer comprises doping the third epitaxial layer with a third dopant having a third concentration, greater than the second concentration, in the third epitaxial layer, and wherein precipitating the second dopant comprises forming a silicide layer through the third epitaxial layer and protruding into the second epitaxial layer.
8. A method, comprising:
forming a fin structure over a substrate;
forming agate structure over the fin structure;
forming a recess structure in the fin structure and adjacent to the gate structure;
forming a first epitaxial layer in the recess structure, wherein forming the first epitaxial layer comprises doping the first epitaxial layer with a first dopant having a first concentration;
forming a second epitaxial layer over the first epitaxial layer, wherein forming the second epitaxial layer comprises doping the second epitaxial layer with a second dopant having a second concentration greater than the first concentration; and
precipitating the second dopant to form a cluster of the second dopant in the second epitaxial layer.
9. The method of claim 8 , wherein:
forming the recess structure comprises forming two opposite side surfaces in the fin structure, wherein the two opposite side surfaces are separated by a lateral separation; and
precipitating the second dopant comprises forming a silicide layer in the second epitaxial layer having a bottom width, wherein a ratio of the bottom width to the lateral separation is from about 0.5 to about 0.9.
10. The method of claim 8 , wherein:
forming the first epitaxial layer comprises epitaxially growing a first silicon germanium layer with a first germanium concentration;
forming the second epitaxial layer comprises epitaxially growing a second silicon germanium layer with a second germanium concentration higher than the first germanium concentration; and
doping the first and the second epitaxial layers comprises flowing a precursor gas containing boron.
11. The method of claim 8 , wherein:
forming the recess structure comprises forming side surfaces in the fin structure,
forming the first epitaxial layer comprises epitaxially growing the first epitaxial layer of a first lateral thickness over the side surfaces;
forming the second epitaxial layer comprises epitaxially growing the second epitaxial layer of a second lateral thickness over the side surfaces; and
a ratio of the first lateral thickness to the second lateral thickness is from about 0.5 to about 1.0.
12. The method of claim 8 ,
wherein the second concentration is between about 5×10 20 /cm 3 and about 6×10 21 /cm 3 , and wherein precipitating the second dopant comprises forming a silicide layer in the second epitaxial layer.
13. The method of claim 8 , wherein precipitating the second dopant comprises forming a silicide layer proximate to the first epitaxial layer, wherein a separation between the silicide layer and the first epitaxial layer is less than about 5 nm.
14. The method of claim 8 , further comprising forming a third epitaxial layer over the second epitaxial layer, wherein:
forming the third epitaxial layer comprises doping the third epitaxial layer with a third dopant having a third concentration less than the second concentration; and
a ratio of a thickness of the third epitaxial layer to a thickness of the second epitaxial layer is from about 0.5 to about 1.0.
15. The method of claim 8 , further comprising:
forming a third epitaxial layer over the second epitaxial layer, wherein forming the third epitaxial layer comprises doping the third epitaxial layer with a third dopant having a third concentration greater than the second concentration; and
precipitating the third dopant from the third epitaxial layer to form a cluster of the third dopant in the third epitaxial layer.
16. A semiconductor structure, comprising:
a substrate;
a fin structure over the substrate;
a gate structure over the fin structure; and
an epitaxial region formed in the fin structure and adjacent to the gate structure, wherein the epitaxial region embeds a plurality of clusters of dopants.
17. The semiconductor structure of claim 16 , wherein each of the plurality of clusters of dopants comprises a plurality of boron atoms proximate to one another.
18. The semiconductor structure of claim 16 , wherein a maximum of an atomic percentage of the dopants in the epitaxial region is from about 2% to about 10%.
19. The semiconductor structure of claim 16 , wherein the epitaxial region comprises:
a first epitaxial layer protruding in the fin structure, wherein the first epitaxial layer comprises a first silicon germanium layer with a first germanium concentration; and
a second epitaxial layer formed over the first epitaxial layer, wherein the second epitaxial layer comprises a second silicon germanium layer with a second germanium concentration greater than the first germanium concentration, and wherein the second epitaxial layer embeds the plurality of clusters of dopants.
20. The semiconductor structure of claim 19 , further comprising a silicide layer formed in the second epitaxial layer, wherein a separation between the silicide layer and the first epitaxial layer is less than about 5 nm.