Nanowire FET including nanowire channel spacers

1. A stacked nanowire field effect transistor (FET) comprising:

a plurality of vertically stacked nanowire channels, each nanowire channel vertically separated from one another by sacrificial segment;

a gate stack on the upper surface of the semiconductor substrate, the gate stack including a conductive element that wraps around the nanowire channels;

source/drain regions on the upper surface of the semiconductor substrate, the source/drain regions directly contacting ends of the nanowire channel; and

nanowire channel spacers that encapsulate the ends of the nanowire channel such that the source/drain regions are separated from the gate stack,

wherein the ends include a first end that extends beneath the gate stack and an opposing second end that contacts inner sidewalls of the source/drain regions.

2. The stacked nanowire FET of claim 1 , wherein the second end stops at the inner sidewalls without extending into the source/drain regions.

3. The stacked nanowire FET of claim 2 , wherein the nanowire channel spacers include intermediate nanowire channel spacers between at least one pair of vertically arranged nanowire channels.

4. The stacked nanowire FET of claim 3 , wherein the intermediate nanowire channel spacers include first sides that contact the inner sidewalls of the source/drain regions and second sides that contact sidewalls of the gate stack.

5. The stacked nanowire FET of claim 4 , wherein first sides directly contact the inner sidewalls of the source/drain regions and the second sides that directly contact the sidewalls of the gate stack.

6. The stacked nanowire FET of claim 1 , wherein the nanowire channel spacers are interposed between the source/drain regions and ends of the sacrificial segment.

7. The stacked nanowire FET of claim 6 , wherein the nanowire channel spacers are interposed between each pair of vertically stacked nanowire channels.

8. The stacked nanowire FET of claim 7 , wherein the nanowire channel spacers comprise a low-dielectric (low-K) material.

9. A method of forming nanowire channel spacers in a nanowire field effect transistor (FET), the method comprising:

forming a multi-stack semiconductor fin on an upper surface of a semiconductor substrate, the multi-stack semiconductor fin comprising a plurality of vertically stacked semiconductor material layers including plurality of nanowire channel layers, each nanowire channel layer vertically separated from one another by a sacrificial layer;

forming source/drain regions on the upper surface of the semiconductor substrate, the source/drain regions contacting the multi-stack fin; and

forming a void that exposes portions of the sacrificial layers and the nanowire channel layers;

etching the exposed portions of the sacrificial layers to form cavities that release opposing ends of the nanowire channel layers and form stacked nanowire channels; and

filing the cavities with a spacer material that encapsulates the released ends and forms the nanowire channel spacers.

10. The method of claim 9 , further comprising forming a gate stack on the upper surface of the semiconductor substrate, the gate stack wrapping around the outer surfaces of the multi-stack semiconductor fin and being separated from the source/drain regions by the void.

11. The method of claim 10 , wherein the nanowire channel spacers are formed with intermediate nanowire channel spacers located between at least one pair of vertically arranged nanowire channels, the intermediate nanowire channel spacers including first sides that directly contact inner sidewalls of the source/drain regions and second sides that directly contact sidewalls of the gate stack.

12. The method of claim 11 , wherein the nanowire channel spacers are interposed between the source/drain regions and the gate stack.

13. The method of claim 12 , wherein forming the source/drain regions further comprises:

forming sacrificial spacers on sidewalls of the gate stack prior to forming the source/drain regions;

after forming the sacrificial spacers, epitaxially growing the source/drain regions such that the sacrificial spacers are interposed between the source/drain regions and the gate stack; and

selectively etching the sacrificial spacers to form the voids that expose the portions of the sacrificial layers and the nanowire channel layers.

14. The method of claim 10 , wherein forming the stacked nanowire channels includes performing a selective etching process that etches the sacrificial layers while maintaining the nanowire channel layers such that the ends are formed with a first end that extends beneath the gate stack and an opposing second end that contacts inner sidewalls and stops thereat.

15. The method of claim 14 , wherein the gate stack comprises a first dielectric material and the sacrificial spacers comprises a second dielectric material different from the first dielectric material.

16. The method of claim 15 , wherein the sacrificial spacers comprise the same dielectric material, and wherein the gate stack includes a gate cap having a first thickness that is greater than a second thickness of the sacrificial spacers.

17. The method of claim 9 , wherein the spacer material comprises a low-dielectric (low-K) material.

18. The method of claim 17 , wherein the sacrificial layers comprise silicon germanium (SiGe) and the nanowire channel layers comprises silicon (Si).

19. A stacked nanowire field effect transistor (FET) comprising:

a plurality of vertically stacked nanowire channels, each nanowire channel vertically separated from one another by sacrificial segment;

a gate stack on the upper surface of the semiconductor substrate, the gate stack including a conductive element that wraps around the nanowire channels;

source/drain regions on the upper surface of the semiconductor substrate, the source/drain regions directly contacting ends of the nanowire channel; and

nanowire channel spacers that encapsulate the ends of the nanowire channel such that the source/drain regions are separated from the gate stack,

wherein the nanowire channel spacers are interposed between the source/drain regions and ends of the sacrificial segment.