Semiconductor device and methods of fabrication thereof
A semiconductor device structure is provided. The semiconductor device structure includes a source/drain epitaxial feature disposed over a substrate, wherein the source/drain epitaxial feature comprises a first epitaxial layer, a second epitaxial layer in contact with the first epitaxial layer, wherein the second epitaxial layer has a first dopant concentration, and a third epitaxial layer having sidewalls enclosed by the second epitaxial layer, wherein the third epitaxial layer has a second dopant concentration higher than the first dopant concentration. The semiconductor device structure also includes a source/drain cap layer disposed above and in contact with the second epitaxial layer and the third epitaxial layer, wherein the source/drain cap layer has a third dopant concentration higher than the second dopant concentration, and a silicide layer disposed above and in contact with the source/drain cap layer.
1 . A semiconductor device structure, comprising:
a source/drain epitaxial feature disposed over a substrate, wherein the source/drain epitaxial feature comprises:
a first epitaxial layer; a second epitaxial layer in contact with the first epitaxial layer, the second epitaxial layer having a first dopant concentration; and a third epitaxial layer having sidewalls enclosed by the second epitaxial layer, the third epitaxial layer having a second dopant concentration higher than the first dopant concentration; a source/drain cap layer disposed above and in contact with the second epitaxial layer and the third epitaxial layer, wherein the source/drain cap layer having has a third dopant concentration higher than the second dopant concentration, and the source/drain cap layer has a first thickness and a silicide layer has a second thickness greater than the first thickness; and the silicide layer disposed above and in contact with the source/drain cap layer.
2 . The semiconductor device structure of claim 1 , wherein the source/drain epitaxial feature is located at a p-type device region of the substrate, and the source/drain cap layer is a boron-doped silicon.
3 . The semiconductor device structure of claim 2 , wherein the source/drain cap layer has an atomic percentage of boron in a range of about 4 at. % to about 15 at. %.
4 . The semiconductor device structure of claim 3 , wherein the third epitaxial layer is a boron-doped silicon germanium having a first boron concentration, and the source/drain cap layer has a second boron concentration that is about 10% to about 30% higher than the first boron concentration.
5 . The semiconductor device structure of claim 4 , wherein the source/drain cap layer further comprises germanium dopants.
6 . The semiconductor device structure of claim 5 , wherein the source/drain cap layer has a first germanium concentration, and the third epitaxial layer has a second germanium concentration higher than the first germanium concentration.
7 . The semiconductor device structure of claim 6 , wherein the silicide layer comprises germanium dopants, and the silicide layer has a third germanium concentration lower than the first germanium concentration.
8 . The semiconductor device structure of claim 1 , wherein the second epitaxial layer has a zig-zag shaped or a saw-tooth shaped profile.
9 . The semiconductor device structure of claim 1 , wherein a bottom of the second epitaxial layer contacting the first epitaxial layer has a first width, and a bottom of the source/drain cap layer contacting the third epitaxial layer has a second width less than the first width.
10 . A semiconductor device structure, comprising:
two or more semiconductor layers stacked vertically over a substrate;
a gate electrode layer surrounding a portion of one of the two or more semiconductor layers;
a source/drain epitaxial feature disposed over the substrate and adjacent the two or more semiconductor layers, the source/drain epitaxial feature comprising:
a first epitaxial layer disposed over the substrate; and
a second epitaxial layer having at least three surfaces in contact with the first epitaxial layer, the second epitaxial layer having a first dopant concentration; and
a source/drain cap layer disposed above and in contact with the first epitaxial layer and the second epitaxial layer, the source/drain cap layer having a second dopant concentration greater than the first dopant concentration, a portion of the source/drain cap layer contacting a first side of the second epitaxial layer defines a first interface, and a portion of the source/drain cap layer contacting a second side of the second epitaxial layer defines a second interface,
wherein the first interface extends along a first direction, the second interface extends along a second direction, and the first direction forms an angle less than about 90 degrees with respect to the second direction;
a silicide layer disposed above and in contact with the source/drain cap layer, wherein a portion of the source/drain cap layer between the second epitaxial layer and the silicide layer has a first thickness, and a portion of the source/drain cap layer between the first epitaxial layer and the silicide layer has a second thickness less than the first thickness.
11 . The semiconductor device structure of claim 10 , wherein the angle is in a range of about 40 degrees to about 80 degrees.
12 . The semiconductor device structure of claim 10 , further comprising:
a facetted structure disposed between and in contact with the source/drain cap layer and a topmost semiconductor layer of the two or more semiconductor layers.
13 . The semiconductor device structure of claim 10 , wherein the source/drain cap layer is a boron-rich silicon, and the third epitaxial layer is a boron-doped silicon germanium.
14 . The semiconductor device structure of claim 13 , wherein the source/drain cap layer has a boron concentration that is about 10% to about 30% higher than a boron concentration of the third epitaxial layer.
15 . A semiconductor device structure, comprising:
two or more semiconductor layers stacked vertically over a substrate;
a gate electrode layer surrounding a portion of one of the two or more semiconductor layers;
a source/drain epitaxial feature disposed over the substrate and adjacent the two or more semiconductor layers, the source/drain epitaxial feature comprising:
a first epitaxial layer disposed over the substrate; and
a second epitaxial layer having at least three surfaces in contact with the first epitaxial layer, the second epitaxial layer having a first dopant concentration; and
a facetted structure disposed on two or more semiconductor layers; and
a source/drain cap layer having a substantially concave profile and in contact with the first epitaxial layer, the second epitaxial layer, and the facetted structure, wherein the source/drain cap layer has a second dopant concentration greater than the first dopant concentration;
a silicide layer disposed above and in contact with the source/drain cap layer, wherein a portion of the source/drain cap layer between the second epitaxial layer and the silicide layer has a first thickness, and a portion of the source/drain cap layer between the first epitaxial layer and the silicide layer has a second thickness less than the first thickness.
16 . The semiconductor device structure of claim 1 , wherein the third dopant concentration is in a range of about 4 at. % to about 15 at. %.
17 . The semiconductor device structure of claim 1 , wherein the source/drain cap layer comprises boron-doped silicon and the third epitaxial layer comprises boron-doped silicon germanium.
18 . The semiconductor device structure of claim 10 , wherein the second dopant concentration is about 10% to about 30% higher than the first dopant concentration.
19 . The semiconductor device structure of claim 15 , wherein the second dopant concentration is in a range of about 4 at. % to about 15 at. %.
20 . The semiconductor device structure of claim 15 , wherein the source/drain cap layer is a boron-rich silicon layer.