Single diffusion breaks including stacked dielectric layers

1. A structure comprising:

a semiconductor fin including a cut and a top surface; and

a single diffusion break including a first dielectric layer in the cut and a second dielectric layer over the first dielectric layer, the first dielectric layer comprised of a first material, the second dielectric layer comprised of a second material having a different composition than the first material, the second dielectric layer including a first portion over the first dielectric layer and a second portion over the first portion, the first portion of the second dielectric layer positioned inside of the cut, the second portion of the second dielectric layer positioned in part over the top surface of the semiconductor fin, the second portion of the second dielectric layer in direct contact with a portion of the top surface of the semiconductor fin, the first portion of the second dielectric layer having a first horizontal dimension, and the second portion of the second dielectric layer having a second horizontal dimension that is greater than the first horizontal dimension.

2. The structure of claim 1 wherein the first material is silicon dioxide, and the second material is a low-k dielectric material.

3. The structure of claim 1 wherein the first material is silicon dioxide, and the second material is carbon-containing silicon nitride.

4. The structure of claim 1 wherein the second portion of the second dielectric layer is positioned outside of the cut.

5. The structure of claim 1 wherein the second portion of the second dielectric layer is fully positioned above the top surface of the semiconductor fin.

6. The structure of claim 1 wherein the first portion of the second dielectric layer is positioned in the cut below the top surface of the semiconductor fin.

7. The structure of claim 1 wherein the first portion of the second dielectric layer is fully positioned in the cut below the top surface of the semiconductor fin.

8. The structure of claim 1 wherein the first horizontal dimension of the first portion of the second dielectric layer is a first width, the second horizontal dimension of the second portion of the second dielectric layer is a second width, the first portion of the second dielectric layer has a first length transverse to the first width, the second portion of the second dielectric layer has a second length transverse to the second width, and the second length is greater than the first length.

9. The structure of claim 8 wherein the first portion of the second dielectric layer is positioned in the cut below the top surface of the semiconductor fin, and the second portion of the second dielectric layer is fully positioned above the top surface of the semiconductor fin.

10. The structure of claim 8 wherein the second portion of the second dielectric layer is positioned outside of the cut.

11. The structure of claim 1 further comprising:

a first gate structure extending across the single diffusion break.

12. The structure of claim 11 further comprising:

a second gate structure extending across the semiconductor fin adjacent to the first gate structure.

13. The structure of claim 12 further comprising:

an epitaxial semiconductor layer coupled to the semiconductor fin, the epitaxial semiconductor layer laterally positioned between the first gate structure and the second gate structure.

14. A structure comprising:

a semiconductor fin including a cut;

a single diffusion break including a first dielectric layer in the cut and a second dielectric layer over the first dielectric layer, the first dielectric layer comprised of a first material, the second dielectric layer comprised of a second material having a different composition than the first material, the second dielectric layer including a first portion over the first dielectric layer and a second portion over the first portion, the first portion of the second dielectric layer having a first horizontal dimension, and the second portion of the second dielectric layer having a second horizontal dimension that is greater than the first horizontal dimension; and

a first gate structure extending across the single diffusion break.

15. The structure of claim 14 further comprising:

a second gate structure extending across the semiconductor fin adjacent to the first gate structure.

16. The structure of claim 15 further comprising:

an epitaxial semiconductor layer coupled to the semiconductor fin, the epitaxial semiconductor layer laterally positioned between the first gate structure and the second gate structure.

17. The structure of claim 14 wherein the first horizontal dimension of the first portion of the second dielectric layer is a first width, the second horizontal dimension of the second portion of the second dielectric layer is a second width, the first portion of the second dielectric layer has a first length transverse to the first width, the second portion of the second dielectric layer has a second length transverse to the second width, and the second length is greater than the first length.

18. The structure of claim 14 wherein the first material is silicon dioxide, and the second material is carbon-containing silicon nitride.

19. A method comprising:

forming a cut in a semiconductor fin; and

forming a single diffusion break including a first dielectric layer in the cut and a second dielectric layer over the first dielectric layer,

wherein the first dielectric layer is comprised of a first material, the second dielectric layer is comprised of a second material having a different composition than the first material, the second dielectric layer includes a first portion over the first dielectric layer and a second portion over the first portion, the first portion of the second dielectric layer has a first horizontal dimension, and the second portion of the second dielectric layer has a second horizontal dimension that is greater than the first horizontal dimension, and

wherein forming the single diffusion break including the first dielectric layer in the cut and the second dielectric layer over the first dielectric layer comprises:

depositing the first dielectric layer inside the cut;

forming a hardmask including an opening positioned over the cut;

recessing the first dielectric layer inside the cut and relative to a top surface of the semiconductor fin with an isotropic etching process; and

widening the opening in the hardmask with the isotropic etching process.

20. The method of claim 19 wherein forming the single diffusion break including the first dielectric layer in the cut and the second dielectric layer over the first dielectric layer further comprises:

depositing the second dielectric layer inside the cut in the semiconductor fin and inside the widened opening in the hardmask; and

removing the hardmask with an etching process.