Replacement material for backside gate cut feature

1. A method comprising:

through a back side of a substrate, removing a portion of a gate structure to form a trench that isolates the gate structure in a first part and a second part, wherein the gate structure elongates along a first direction, the first part of the gate structure comprises a sidewall exposed to the trench and extending along a plane perpendicular to the first direction;

depositing a sacrificial material within the trench and conformally along sidewalls of the trench;

filling a remainder of the trench with a first dielectric material;

partially removing the sacrificial material to leave an opening between the first dielectric material and the gate structure; and

filling the opening with a work-function metal.

2. The method of claim 1 , further comprising, partially removing the work-function metal from the opening.

3. The method of claim 2 , further comprising, filling a remainder of the opening with a second dielectric material.

4. The method of claim 3 , wherein the second dielectric material is an oxide material.

5. The method of claim 1 , wherein filling the opening with the work-function metal includes depositing the work-function metal to entirely overlap sidewalls of the first and the second parts of the gate structure with respect to a cross-sectional view.

6. The method of claim 5 , wherein the removing of the portion of the gate structure includes partially etching an upper layer over the gate structure.

7. The method of claim 6 , wherein the trench extends into the upper layer by about 2-15 nanometers.

8. The method of claim 1 , wherein a width of the trench is within a range of about 7-40 nanometers at a region corresponding to the gate structure.

9. The method of claim 1 , wherein a width of the trench is within a range of about 21-54 nanometers at a region corresponding to below the gate structure.

10. The method of claim 1 , wherein a distance from a sidewall of the trench and a nanostructure is within a range of about 3-20 nanometers.

11. A method comprising:

etching a gate structure over a substrate to form a trench through the gate structure;

conformally depositing a sacrificial layer within the trench;

depositing a dielectric layer over the sacrificial layer;

removing the sacrificial layer; and

filling a void left by removing the sacrificial layer with a work-function metal material.

12. The method of claim 11 , wherein the filling of the void includes depositing the work-function metal material to directly contact a spacer feature along a sidewall of a fin structure.

13. The method of claim 11 , wherein the trench is parallel with at least one fin structure extending from the substrate.

14. The method of claim 11 , wherein the trench extends along a central line between two adjacent fin structures.

15. The method of claim 11 , wherein the trench is away from a central line between two adjacent fin structures.

16. The method of claim 11 , wherein the sacrificial layer comprises aluminum oxide.

17. The method of claim 11 , further comprising: depositing a dielectric material over the gate structure before etching the gate structure.

18. A method comprising:

through a back side of a substrate, removing a portion of a gate structure to form a trench that isolates the gate structure in two portions;

conformally depositing a sacrificial material within the trench;

after the conformally depositing of the sacrificial material, depositing a first dielectric material within the trench; and

after the depositing of the first dielectric material, replacing a portion of the sacrificial material that extends along a sidewall surface of the first dielectric material with a work-function metal material.

19. The method of claim 18 , further comprising, replacing a portion of the work-function metal material with a second dielectric material.

20. The method of claim 18 , wherein the work-function metal material includes a same material as a material in the gate structure.