Gate-all around transistor with isolating feature under source/drain
Semiconductor structures and methods for manufacturing the same are provided. The semiconductor structure includes semiconductor material layers stacked above a substrate along a first direction and a gate structure wrapping around the semiconductor material layers. The semiconductor structure further includes an epitaxial structure coupled to the semiconductor material layers in a second direction that is different from the first direction and a SiGe-containing layer located below the epitaxial structure. In addition, a material of the SiGe-containing layer is different from a material of the epitaxial structure, the SiGe-containing layer comprises a first portion with a first thickness in the first direction, and a second portion with a second thickness in the first direction, and the second thickness is smaller than the first thickness.
1 . A semiconductor structure, comprising:
semiconductor material layers stacked above a substrate along a first direction;
a gate structure wrapping around the semiconductor material layers;
an epitaxial structure coupled to the semiconductor material layers in a second direction that is different from the first direction; and
a SiGe-containing layer located below the epitaxial structure, wherein:
a material of the SiGe-containing layer is different from a material of the epitaxial structure,
the SiGe-containing layer comprises a first portion with a first thickness in the first direction, and a second portion with a second thickness in the first direction, and the second thickness is smaller than the first thickness, and
the SiGe-containing layer is partially sandwiched between the epitaxial structure and the gate structure in the second direction.
2 . The semiconductor structure as claimed in claim 1 , wherein the SiGe-containing layer has a curved bottom surface.
3 . The semiconductor structure as claimed in claim 1 , wherein the gate structure has a top portion over the semiconductor material layers and a bottom portion under the semiconductor material layers, and a dimension of the top portion of the gate structure is different from a dimension of the bottom portion of the gate structure in the second direction.
4 . The semiconductor structure as claimed in claim 3 , wherein the dimension of the top portion of the gate structure is smaller than the dimension of the bottom portion of the gate structure in the second direction.
5 . The semiconductor structure as claimed in claim 1 , wherein the SiGe-containing layer is separated from the semiconductor material layers.
6 . The semiconductor structure as claimed in claim 1 , wherein a curved interface is between the SiGe-containing layer and the epitaxial structure.
7 . The semiconductor structure as claimed in claim 1 , further comprising:
a dielectric structure covering a sidewall of the SiGe-containing layer.
8 . The semiconductor structure as claimed in claim 1 , wherein a width of the epitaxial structure is greater than a width of the SiGe-containing layer in a cross-sectional view.
9 . A semiconductor structure, comprising:
a substrate;
epitaxial structures over the substrate;
semiconductor material layers laterally extending between the epitaxial structures;
a gate structure wrapping around the semiconductor material layers;
semiconductor features under the epitaxial structures, wherein the semiconductor features comprise a material different from a material of the epitaxial structures, and an interface between the semiconductor features and the epitaxial structures is lower than the semiconductor material layers; and
fin spacers covering opposite sides of the semiconductor features and vertically under the epitaxial structures.
10 . The semiconductor structure as claimed in claim 9 , further comprising:
a base structure protruding from the substrate and under the semiconductor material layers, wherein a curved interface is in between the base structure and the semiconductor features.
11 . The semiconductor structure as claimed in claim 9 , wherein at least one of the semiconductor material layers has a sloped sidewall.
12 . The semiconductor structure as claimed in claim 9 , wherein the semiconductor material layers comprise:
a bottom semiconductor material layer;
a middle semiconductor material layer over the bottom semiconductor material layer; and
a top semiconductor material layer over the middle semiconductor material layer,
wherein the bottom semiconductor material layer is wider than the middle semiconductor material layer in a cross-sectional view.
13 . The semiconductor structure as claimed in claim 12 , wherein the middle semiconductor material layer is wider than the top semiconductor material layer in the cross-sectional view.
14 . A semiconductor structure, comprising:
a substrate;
semiconductor material layers stacked along a first direction over the substrate and spaced apart from each other;
a gate structure wrapping around the semiconductor material layers;
an epitaxial structure coupled to the semiconductor material layers in a second direction different from the first direction; and
a semiconductor feature under the epitaxial structure, wherein the semiconductor feature has a bottom surface that is lower than a top surface of the semiconductor material layers, and the bottom surface of the semiconductor feature has a curved shape in a cross-sectional view in a third direction that is different from the first direction and the second direction.
15 . The semiconductor structure as claimed in claim 14 , wherein the semiconductor feature is made of SiGe and the epitaxial structure is made of SiP.
16 . The semiconductor structure as claimed in claim 14 , further comprising:
dielectric features separated with each other in the first direction, wherein at least one of the dielectric features is in contact with the semiconductor feature.
17 . The semiconductor structure as claimed in claim 14 , wherein the semiconductor material layers comprise varying widths.
18 . The semiconductor structure as claimed in claim 14 , further comprising:
base structure protruding from the substrate and extending in the second direction; and
an isolation structure around the base structure,
wherein the gate structure extends in the third direction and covers the isolation structure in the first direction.
19 . The semiconductor structure as claimed in claim 18 , wherein the base structure has slope sidewalls in the cross-sectional view in the third direction.
20 . The semiconductor structure as claimed in claim 19 , wherein the semiconductor feature intersects with the slope sidewalls of the base structures.