Methods and structures for forming field-effect transistors (FETs) with low-k spacers

1. A method for manufacturing a semiconductor device, comprising:

forming a sacrificial dielectric layer on a substrate;

forming a plurality of dummy gate patterns spaced apart from each other on the sacrificial dielectric layer;

removing exposed portions of the sacrificial dielectric layer adjacent the plurality of dummy gate patterns;

growing a plurality of source/drain regions adjacent the plurality of dummy gate patterns;

forming a dielectric layer on each of the plurality of source/drain regions adjacent the plurality of dummy gate patterns;

removing the plurality of dummy gate patterns to create a plurality of trenches;

forming a plurality of spacers on sidewalls of each of the plurality of trenches, wherein the plurality of spacers comprise at least one of a low-k material and an airgap; and

forming a gate structure in each of the plurality of trenches between the plurality of spacers.

2. The method according to claim 1 , wherein a width of each dummy gate pattern comprises at least a width of the gate structure and a combined width of the spacers on either side of the gate structure for each trench of the plurality of trenches.

3. The method according to claim 1 , further comprising removing a portion of the sacrificial dielectric layer in each of the plurality of trenches to expose portions the substrate.

4. The method according to claim 3 , wherein the removed portion of the sacrificial dielectric layer includes parts of the sacrificial dielectric layer under the spacers in each trench of the plurality of trenches, wherein an undercut region is formed under each spacer.

5. The method according to claim 4 , further comprising forming a gate dielectric layer on the plurality of spacers, in the undercut region formed under each spacer and on the exposed portions of the substrate in each of the plurality of trenches, wherein the gate structure is formed on the gate dielectric layer in each of the plurality of trenches.

6. The method according to claim 1 , further comprising:

recessing the plurality of spacers and the gate structure in each of the plurality of trenches; and

forming a dielectric cap layer on each of the recessed spacers and each gate structure.

7. The method according to claim 1 , further comprising:

depositing a co-polymer in each of the plurality of trenches; and

annealing the co-polymer in each of the plurality of trenches to separate each co-polymer into a first polymer layer positioned between second polymer layers on opposite lateral sides of the first polymer layer.

8. The method according to claim 7 , further comprising selectively removing the second polymer layers from each of the plurality of trenches.

9. The method according to claim 8 , wherein forming the plurality of spacers comprises depositing spacer material into spaces in each of the plurality of trenches left by the selective removal of the second polymer layers.

10. The method according to claim 9 , further comprising selectively removing the first polymer layer from each of the plurality of trenches.

11. The method according to claim 1 , further comprising:

depositing a dummy spacer layer on the sidewalls and on the sacrificial dielectric layer in each of the plurality of trenches; and

depositing a dielectric layer on the dummy spacer layer in each of the plurality of trenches.

12. The method according to claim 11 , further comprising recessing the dielectric layer on the dummy spacer layer in each of the plurality of trenches.

13. The method according to claim 12 , further comprising removing exposed portions of the dummy spacer layer from each of the plurality of trenches.

14. The method according to claim 13 , wherein forming the plurality of spacers comprises depositing spacer material in spaces in each of the plurality of trenches left by the removal of the exposed portions of the dummy spacer layer.

15. The method according to claim 14 , wherein a resulting thickness of the deposited spacer material with respect to the sidewalls varies in each of the plurality of trenches.

16. The method according to claim 15 , wherein the resulting thickness of the deposited spacer material is greater near the recessed dielectric layer on the dummy spacer layer than at portions above the recessed dielectric layer in each of the plurality of trenches.

17. The method according to claim 1 , wherein a width of the gate structure varies in each of the plurality of trenches.

18. A semiconductor device, comprising:

a plurality of gate structures spaced apart from each other on a substrate;

a plurality of source/drain regions adjacent the plurality of gate structures;

a plurality of spacers on sidewalls of each of the plurality of gate structures, wherein the plurality of spacers comprise at least one of a low-k material and an airgap; and

a gate dielectric layer formed between each of the plurality of spacers and a corresponding gate structure, wherein the gate dielectric layer is further formed in an undercut region under each of the plurality of spacers, and on the substrate between the substrate and the corresponding gate structure.

19. The semiconductor device according to claim 18 , wherein a width of each of the plurality of gate structures is greater in an upper portion of each gate structure than in a lower portion of each gate structure closer to the substrate.