Semiconductor device structures
In one exemplary aspect, a method for semiconductor manufacturing comprises forming first and second silicon nitride features on sidewall surfaces of a contact hole, where the contact hole is disposed in a dielectric layer and above a source/drain (S/D) feature. The method further comprises forming a contact plug in the contact hole, the contact plug being electrically coupled to the S/D feature, removing a top portion of the contact plug to create a recess in the contact hole, forming a hard mask layer in the recess, and removing the first and second silicon nitride features via selective etching to form first and second air gaps, respectively.
1. A method for semiconductor manufacturing, comprising:
forming first and second silicon nitride features on sidewall surfaces of a contact hole, the contact hole being disposed in a dielectric layer and above a source/drain (S/D) feature;
forming a contact plug in the contact hole, the contact plug being electrically coupled to the S/D feature;
removing a top portion of the contact plug to create a recess in the contact hole;
forming a hard mask layer in the recess; and
removing the first and second silicon nitride features via selective etching to form first and second air gaps, respectively.
2. The method of claim 1 , wherein the first air gap is formed between the contact plug and the dielectric layer to reduce a first capacitance between the contact plug and a first neighboring gate stack, and wherein the second air gap is formed between the contact plug and the dielectric layer to reduce a second capacitance between the contact plug and a second neighboring gate stack.
3. The method of claim 2 , wherein the first and second air gaps are formed such that the contact plug is directly exposed to the first and second air gaps.
4. The method of claim 2 , wherein the dielectric layer is a first inter-layer dielectric (ILD) layer, and wherein the method further comprises forming over the contact plug a second ILD layer that covers the first and second air gaps.
5. The method of claim 4 , wherein the second ILD layer interfaces the first and second air gaps at a height that is above top surfaces of the first and second neighboring gate stacks.
6. The method of claim 5 , wherein the first and second air gaps are separated from the first and second neighboring gate stacks, respectively, by at least the first ILD layer which includes a low-k material.
7. The method of claim 1 , wherein forming the hard mask layer in the recess comprises:
depositing the hard mask layer; and
removing a top portion of the hard mask layer using a chemical mechanical planarization (CMP) process, wherein the CMP process exposes top surfaces of the first and second silicon nitride features to facilitate the removal of the first and second silicon nitride features.
8. The method of claim 7 , wherein a remaining thickness of the hard mask layer in the recess after the CMP process is 2-5 nm, and wherein the recess is at least 3 nm above a neighboring gate stack of the contact plug.
9. The method of claim 1 , wherein the contact plug comprises a barrier layer and a metal fill layer, and wherein forming the contact plug comprises:
forming the barrier layer between the first and second silicon nitride features;
depositing the metal fill layer covering the barrier layer and the dielectric layer; and
removing a top portion of the metal fill layer using a chemical mechanical planarization (CMP) process.
10. The method of claim 1 , wherein the first and second silicon nitride features have etch selectivity such that the first and second silicon nitride features are removable at a rate at least 10 times faster than other materials in contact with the first and second silicon nitride features.
11. A method, comprising:
providing a semiconductor device structure including:
a substrate;
first and second gate stacks on the substrate;
first and second silicon nitride features disposed on sidewall surfaces of a contact hole defined in and surrounded by a dielectric layer between the first and second gate stacks;
a barrier layer formed of a material different than silicon nitride and disposed on lower portions of the first and second silicon nitride features; and
a metal fill layer including a top portion and a bottom portion, wherein the top portion is in direct contact with the first and second nitride features and the bottom portion is in direct contact with the barrier layer;
etching the first and second silicon nitride features, without substantially etching the barrier layer, to form first and second air gaps, respectively, wherein the first and second air gaps expose sidewalls of the metal fill layer to air within the first and second air gaps; and
forming a seal layer over the metal fill layer to cover the first and second air gaps.
12. The method of claim 11 , wherein the seal layer interfaces the first and second air gaps at a height that is above top surfaces of the first and second gate stacks.
13. The method of claim 12 , wherein the seal layer is formed using a physical vapor deposition (PVD) process such that the seal layer interfaces the first and second air gaps at a height that is no greater than 5 nm below a top surface of the metal fill layer.
14. The method of claim 11 , wherein the first and second air gaps both have a width between 1-5 nm, and wherein the first and second air gaps are separated from the first and second gate stacks, respectively, by at least an interlayer dielectric (ILD) layer that includes a low-k material.
15. The method of claim 11 , wherein the metal fill layer is separated from the first gate stack by the first air gap.
16. A method, comprising:
forming first and second silicon nitride features on sidewall surfaces of a contact hole, the contact hole being disposed in a dielectric layer and above a source/drain (S/D) feature;
forming a contact plug in the contact hole, the contact plug being electrically coupled to the S/D feature and comprising:
a barrier layer, and
a metal fill layer over the barrier layer such that a top portion of the metal fill layer is in direct contact with the first and second silicon nitride features and a bottom portion of the metal fill layer is spaced apart from the first and second silicon nitride features by the barrier layer; and
removing the first and second silicon nitride features via selective etching to form first and second air gaps, respectively.
17. The method of claim 16 , wherein the forming of the contact plug comprises:
depositing the barrier layer over the contact hole;
etching the barrier layer to expose top portions of sidewalls of the first and second silicon nitride features; and
after the etching of the barrier layer, depositing the metal fill layer over the barrier layer.
18. The method of claim 17 , further comprising:
cleaning the etched barrier layer to form a tapered thickness profile of the barrier layer,
wherein the tapered thickness profile comprises a first thickness of an upper portion of the barrier layer and a second thickness of a bottom portion of the barrier layer,
wherein the second thickness is greater than the first thickness.
19. The method of claim 17 , wherein the forming of the barrier layer comprises:
depositing a metal layer in contact with the S/D feature, the first silicon nitride feature, and the second silicon nitride feature; and
annealing the metal layer to form a metal silicide in contact with the S/D feature and the barrier layer in contact with the first and second nitride features.
20. The method of claim 19 , wherein the metal layer comprises titanium or tantalum and the barrier layer comprises titanium nitride or tantalum nitride.