BEOL interconnect structures and related fabrication methods

1. A method for fabricating a back-end-of-line (BEOL) interconnect structure, the method comprising:

forming a first temporary feature on a top surface of a first dielectric layer;

depositing a second dielectric layer comprised of a first dielectric material on the top surface of the first dielectric layer;

planarizing the second dielectric layer and the first temporary feature such that a layer thickness of the second dielectric layer is approximately equal to a height of the first temporary feature;

forming a first conductive feature that extends from a top surface of the second dielectric layer to a conductive element in the first dielectric layer and that is located in the second dielectric layer laterally adjacent to the first temporary feature;

removing the first temporary feature from the second dielectric layer to define a first void in the second dielectric layer laterally adjacent to the first conductive feature; and

filling the first void formed in the second dielectric layer with a second dielectric material that has a lower dielectric constant than the first dielectric material of the second dielectric layer.

2. The method of claim 1 wherein removing the first temporary feature from the second dielectric layer to define a first void in the second dielectric layer further comprises:

depositing a hardmask layer on a top surface of the second dielectric layer;

patterning the hardmask layer to define a window spatially registered with the first temporary feature; and

selectively etching the first temporary feature relative to the second dielectric layer so that the first void is formed in the second dielectric layer.

3. The method of claim 2 further comprising:

depositing a third dielectric layer on a top surface of the hardmask layer to occlude the window.

4. The method of claim 1 wherein removing the first temporary feature from the second dielectric layer to define the first void in the second dielectric layer comprises:

selectively etching a sacrificial material comprising the first temporary feature relative to the first and second dielectric layers.

5. The method of claim 1 wherein further comprising:

forming a second conductive feature that extends from the top surface of the second dielectric layer to the top surface of the first dielectric layer and that is located in the second dielectric layer such that the first temporary feature is laterally located between the first and second conductive features.

6. The method of claim 1 wherein the first temporary feature is comprised of a sacrificial material that etches selectively to a third dielectric material forming the first dielectric layer, and forming the first temporary feature on the top surface of the first dielectric layer comprises:

depositing a layer of the sacrificial material on the top surface of the first dielectric layer;

forming a patterned etch mask on a top surface of the layer of the sacrificial material; and

etching portions of the layer of the sacrificial material exposed by the patterned etch mask to define the first temporary feature.

7. The method of claim 1 further comprising:

before the second dielectric layer is deposited, forming a second temporary feature on the top surface of the first dielectric layer that is laterally separated from the first temporary feature by the first conductive feature and that has approximately equal height to the first temporary feature; and

when the first temporary feature is removed, removing the second temporary feature from the second dielectric layer to define a second void in the second dielectric layer.

8. The method of claim 7 further comprising:

when the first void is filled, filling the second void formed in the second dielectric layer with the second dielectric material that has the lower dielectric constant than the first dielectric material of the second dielectric layer.

9. The method of claim 7 wherein removing the second temporary feature from the second dielectric layer to define the second void in the second dielectric layer further comprises:

depositing a hardmask layer on a top surface of the second dielectric layer;

patterning the hardmask layer to define a window spatially registered with the second temporary feature; and

selectively etching the second temporary feature relative to the second dielectric layer so that the second void is formed in the second dielectric layer.

10. The method of claim 9 further comprising:

depositing a third dielectric layer on a top surface of the hardmask layer to occlude the window; and

when the hardmask layer is patterned, selecting dimensions of the window such that a portion of the third dielectric layer will occlude the window in the hardmask and close the first void so that a majority of the first void is unfilled by a fourth dielectric material from the third dielectric layer.

11. The method of claim 1 wherein the first temporary feature is formed on the top surface of the first dielectric layer before the second dielectric layer is deposited.

12. The method of claim 1 further comprising:

before the second dielectric layer is deposited, forming a second temporary feature on the top surface of the first dielectric layer that is laterally separated from the first temporary feature by the first conductive feature and that has approximately equal height to the first temporary feature.

13. The method of claim 12 wherein depositing the second dielectric layer comprised of the first dielectric material on the top surface of the first dielectric layer comprises:

filling a space laterally between the first temporary feature and the second temporary feature with a portion of the second dielectric material of the second dielectric layer.

14. The method of claim 1 wherein the first temporary feature is comprised of polycrystalline silicon.

15. The method of claim 1 wherein the second dielectric material is a porous oxide, an organic polymer, non-porous hydrogen-enriched silicon oxycarbide (SiCOH), or carbon doped oxide (CDO).

16. The method of claim 1 wherein removing the first temporary feature from the second dielectric layer to define a first void in the second dielectric layer further comprises:

forming a resist layer on a top surface of the second dielectric layer;

patterning the resist layer to define a window spatially registered with the first temporary feature; and

selectively etching the first temporary feature relative to the second dielectric layer so that the first void is formed in the second dielectric layer.

17. The method of claim 16 further comprising:

removing the resist layer; and

after the first void is filled with the second dielectric material, depositing a third dielectric layer on a top surface of the second dielectric layer to occlude the window.