Backside contact
A semiconductor structure and a method of forming the same are provided. In an embodiment, a semiconductor structure includes an epitaxial source feature and an epitaxial drain feature, a vertical stack of channel members disposed over a backside dielectric layer, the vertical stack of channel members extending between the epitaxial source feature and the epitaxial drain feature along a direction, a gate structure wrapping around each of the vertical stack of channel members, and a backside source contact disposed in the backside dielectric layer. The backside source contact includes a top portion adjacent the epitaxial source feature and a bottom portion away from the epitaxial source feature. The top portion and the bottom portion includes a step width change along the direction.
1 . A method, comprising:
forming, over a substrate, a stack including a plurality of channel layers interleaved by a plurality of sacrificial layers;
patterning the stack and the substrate to form a fin-shaped structure;
forming a source opening and a drain opening;
depositing a dummy epitaxial feature in the source opening and the drain opening;
forming a source feature in the source opening and a drain feature in the drain opening, the source feature and the drain feature being disposed over the dummy epitaxial feature;
anisotropically etching the substrate to form a backside contact opening exposing the dummy epitaxial feature over the source feature;
selectively and isotropically etching the dummy epitaxial feature; and
forming a backside source contact in the backside contact opening to couple to the source feature.
2 . The method of claim 1 , wherein the anisotropically etching comprises use of hydrogen bromide, oxygen or chlorine.
3 . The method of claim 1 , wherein the selectively and isotropically etching comprises use of fluorine and hydrogen fluoride.
4 . The method of claim 1 , further comprising:
before the forming of the source feature and the drain feature, depositing an epitaxial layer over the dummy epitaxial feature.
5 . The method of claim 4 , further comprising:
before the forming of the backside source contact, depositing a dielectric barrier layer over the source opening; and
etching back the dielectric barrier layer,
wherein the etching back also removes the epitaxial layer over the source feature.
6 . A method, comprising:
forming, over a substrate, a stack including a plurality of channel layers interleaved by a plurality of sacrificial layers;
patterning the stack and the substrate to form a fin-shaped structure that includes a stack portion patterned from the stack and a base portion patterned from the substrate;
forming a source opening and a drain opening through the stack portion;
depositing a dummy epitaxial feature in the source opening and the drain opening;
forming a source feature in the source opening and a drain feature in the drain opening, the source feature and the drain feature being disposed over the dummy epitaxial feature;
anisotropically etching the substrate to form a backside contact opening exposing the dummy epitaxial feature over the source feature;
selectively and isotropically etching the dummy epitaxial feature; and
forming a backside source contact in the backside contact opening to couple to the source feature,
wherein a composition of the dummy epitaxial feature is different from a composition of the substrate.
7 . The method of claim 6 , wherein the dummy epitaxial feature comprises silicon germanium.
8 . The method of claim 6 , further comprising:
forming an isolation feature over the substrate to interface sidewalls of the base portion.
9 . The method of claim 8 , wherein the dummy epitaxial feature is deposited such that a top surface of the dummy epitaxial feature does not rise above a top surface of the isolation feature.
10 . The method of claim 6 , wherein the anisotropically etching comprises use of hydrogen bromide, oxygen or chlorine.
11 . The method of claim 6 , wherein the selectively and isotropically etching comprises use of fluorine and hydrogen fluoride.
12 . The method of claim 6 , further comprising:
before the forming of the backside source contact, depositing a dielectric barrier layer over the source opening; and
etching back the dielectric barrier layer to expose the source feature in the backside contact opening.
13 . The method of claim 12 , wherein the dielectric barrier layer comprises silicon nitride.
14 . The method of claim 6 , wherein the forming of the backside source contact comprises:
forming a silicide feature over and interfacing the source feature; and
depositing a metal fill layer over the silicide feature.
15 . The method of claim 14 ,
wherein the silicide feature comprises titanium silicide (TiSi), titanium silicon nitride (TiSiN), tantalum silicide (TaSi), tungsten silicide (WSi), cobalt silicide (CoSi), or nickel silicide (NiSi),
wherein the metal fill layer comprises tungsten (W), ruthenium (Ru), copper (Cu), cobalt (Co), titanium (Ti), titanium nitride (TiN), tantalum (Ta), titanium nitride (TaN), molybdenum (Mo), or nickel (Ni).
16 . A method, comprising:
forming, over a substrate, a stack including a plurality of channel layers interleaved by a plurality of sacrificial layers;
patterning the stack and the substrate to form a fin-shaped structure that includes a stack portion patterned from the stack and a base portion patterned from the substrate;
forming a source opening and a drain opening through the stack portion, the source opening and the drain opening partially extending into the base portion;
depositing a dummy epitaxial feature in the source opening and the drain opening;
forming a source feature in the source opening and a drain feature in the drain opening, the source feature and the drain feature being disposed over the dummy epitaxial feature;
forming a patterned hard mask over the substrate, the patterned hard mask comprising an opening vertically aligned with the source feature;
anisotropically etching the substrate using the patterned hard mask as an etch mask to form a backside contact opening exposing the dummy epitaxial feature over the source feature;
selectively and isotropically etching the dummy epitaxial feature; and
forming a backside source contact in the backside contact opening to couple to the source feature.
17 . The method of claim 16 , wherein a composition of the dummy epitaxial feature is different from a composition of the substrate.
18 . The method of claim 16 , wherein the dummy epitaxial feature comprises silicon germanium.
19 . The method of claim 16 , further comprising:
forming an isolation feature over the substrate to interface sidewalls of the base portion,
wherein the source feature and the drain feature.
20 . The method of claim 16 , further comprising:
before the forming of the backside source contact, depositing a dielectric barrier layer over the source opening; and
etching back the dielectric barrier layer to expose the source feature in the backside contact opening.