Isolated fin structures in semiconductor devices
A semiconductor device and a method of forming the same are disclosed. The method includes forming a fin with a sacrificial layer on a semiconductor substrate, forming isolation regions on the semiconductor substrate and adjacent to the fin, forming a superlattice structure with first and second nanostructured layers on the sacrificial layer, forming a sacrificial structure that surrounds the superlattice structure, forming a first spacer on the superlattice structure, forming an air gap between the superlattice structure and the fin, and forming a second spacer on the fin and below the superlattice structure.
1. A method, comprising:
forming a fin with a sacrificial layer on a semiconductor substrate;
forming isolation regions on the semiconductor substrate and adjacent to the fin;
forming a superlattice structure with first and second nanostructured layers on the sacrificial layer;
forming a sacrificial structure that surrounds the superlattice structure;
forming a first spacer on the superlattice structure and the isolation regions;
forming an air gap between the superlattice structure and the fin after forming the first spacer; and
forming a second spacer on the fin and below the superlattice structure.
2. The method of claim 1 , wherein forming the air gap comprises etching top surfaces of the isolation regions.
3. The method of claim 1 , wherein forming the air gap comprises etching the sacrificial layer.
4. The method of claim 1 , wherein forming the air gap comprises etching portions of the isolation regions adjacent to the sacrificial layer.
5. The method of claim 1 , wherein forming the air gap comprises etching portions of the isolation regions to expose sidewalls of the portions of the sacrificial layer that are not under the sacrificial structure.
6. The method of claim 1 , further comprising growing source/drain regions from the first or second nanostructured layers.
7. The method of claim 1 , wherein forming the first spacer on the superlattice structure comprises forming the first spacer on portions of the superlattice structure that are not covered by the sacrificial structure.
8. The method of claim 1 , further comprising:
removing a portion of the first spacer; and
growing source/drain regions from the first or second nanostructured layers.
9. The method of claim 1 , wherein forming the second spacer comprises depositing a dielectric layer on the isolation regions.
10. The method of claim 1 , wherein forming the second spacer comprises depositing a dielectric layer within the air gap and on the fin.
11. A method, comprising:
forming a fin with a sacrificial layer on a substrate;
forming isolation regions on the substrate and adjacent to the fin;
forming a stack of first and second nanostructured layers on the sacrificial layer;
forming a polysilicon structure surrounding the stack of first and second nanostructured layers, the polysilicon structure defining a gate length;
forming a first spacer surrounding the stack of first and second nanostructured layers;
forming an air gap between the fin and the stack of first and second nanostructured layers after forming the first spacer;
replacing portions of the stack of first and second nanostructured layers not covered by the polysilicon structure with epitaxial source/drain regions; and
replacing the polysilicon structure with a gate structure.
12. The method of claim 11 , wherein forming the air gap comprises etching portions of the isolation regions adjacent to the sacrificial layer.
13. The method of claim 11 , further comprising etching the second nanostructured layers.
14. The method of claim 11 , further comprising forming an etch stop layer within the air gap.
15. The method of claim 11 , wherein forming the air gap comprises forming the air gap with a height in a range of about 1 nm to about 30 nm.
16. The method of claim 15 , wherein forming the air gap comprises forming the air gap with a width substantially equal to the gate length, a height that ranges from about 1 nm to about 30 nm, and an aspect ratio that ranges from about 0.2:1 to about 1:1.
17. A method, comprising:
forming a fin on a substrate;
epitaxially growing a semiconductor layer on a top surface of the fin;
epitaxially growing nanostructured layers on the semiconductor layer;
forming a first spacer directly on sidewalls of the nanostructured layers;
removing the semiconductor layer to expose the top surface of the fin while the sidewalls of the nanostructured layers are covered by the first spacer;
forming a second spacer on the exposed top surface of the fin;
forming a source/drain (S/D) region suspended on the fin; and
forming a gate structure surrounding the nanostructured layers.
18. The method of claim 17 , further comprising etching the first spacer to form sidewall spacers adjacent to the S/D region.
19. The method of claim 18 , wherein etching the first spacer comprises etching a top portion of the first spacer to form the sidewall spacers.
20. The method of claim 17 , further comprising forming a third spacer disposed on a bottom surface of the nanostructured layers.