Fabricating gate-all-around transistors having high aspect ratio channels and reduced parasitic capacitance

1. A method of fabricating a semiconductor device, the method comprising:

forming a fin over a substrate;

wherein the fin comprises an upper fin region and a lower fin region;

wherein the lower fin region is physically coupled to the upper fin region and the substrate;

removing a portion of the fin to form a fin tunnel configured to physically separate the upper fin region from the lower fin region; and

forming a gate structure configured to fill the fin tunnel and cover a top surface, a bottom surface, a first sidewall, and a second sidewall of the upper fin region.

2. The method of claim 1 , wherein the gate structure comprises a gate dielectric and a conductive gate material.

3. The method of claim 2 , wherein the gate dielectric is on the top surface, the bottom surface, the first sidewall, and the second sidewall of the upper fin region.

4. The method of claim 3 , wherein the conductive gate material is on the gate dielectric.

5. The method of claim 4 , wherein the gate dielectric comprises a high-k dielectric.

6. The method of claim 1 , wherein:

isolation regions cover sidewalls of the lower fin region; and

removing the portion of the fin comprises:

depositing a protective mask over the upper fin region leaving unprotected an exposed portion of the first sidewall of the upper fin region and an exposed portion of the second sidewall of the upper fin region; and

applying an etchant to the exposed portion of the first sidewall of the upper fin region and the exposed portion of the second sidewall of the upper fin region.

7. The method of claim 1 further comprising:

communicatively coupling a first source or drain (S/D) region to a first end sidewall of the upper fin region; and

communicatively coupling a second S/D region to a second end sidewall of the upper fin region;

wherein the upper fin region functions as a channel region of the semiconductor device.

8. A method of fabricating a semiconductor device, the method comprising:

forming a first fin and a second fin over a substrate;

wherein the first fin comprises an upper first fin region and a lower first fin region;

wherein the lower first fin region is physically coupled to the upper first fin region and the substrate;

wherein the second fin comprises an upper second fin region and a lower second fin region;

wherein the lower second fin region is physically coupled to the upper second fin region and the substrate;

removing a portion of the first fin to form a first fin tunnel configured to physically separate the upper first fin region from the lower first fin region;

removing a portion of the second fin to form a second fin tunnel configured to physically separate the upper second fin region from the lower second fin region; and

forming a gate structure configured to:

fill the first fin tunnel;

fill the second tunnel;

cover a top surface, a bottom surface, a first sidewall, and a second sidewall of the upper first fin region; and

cover a top surface, a bottom surface, a first sidewall, and a second sidewall of the upper second fin region.

9. The method of claim 8 , wherein the gate structure comprises a gate dielectric and a conductive gate material.

10. The method of claim 9 , wherein the gate dielectric is on:

the top surface, the bottom surface, the first sidewall, and the second sidewall of the upper first fin region; and

the top surface, the bottom surface, the first sidewall, and the second sidewall of the upper second fin region.

11. The method of claim 10 , wherein the conductive gate material is on the gate dielectric.

12. The method of claim 11 , wherein the gate dielectric comprises a high-k dielectric.

13. The method of claim 8 , wherein:

isolation regions cover sidewalls of the lower first fin region and sidewalls of the lower second fin region;

removing the portion of the first fin comprises:

depositing a first protective mask over the upper first fin region leaving unprotected an exposed portion of the first sidewall of the upper first fin region and an exposed portion of the second sidewall of the upper first fin region; and

applying an etchant to the exposed portion of the first sidewall of the upper first fin region and the exposed portion of the second sidewall of the upper first fin region; and

removing the portion of the second fin comprises:

depositing a second protective mask over the upper second fin region leaving unprotected an exposed portion of the first sidewall of the upper second fin region and an exposed portion of the second sidewall of the upper second fin region; and

applying an etchant to the exposed portion of the first sidewall of the upper second fin region and the exposed portion of the second sidewall of the upper second fin region.

14. The method of claim 8 further comprising:

communicatively coupling a first source or drain (S/D) region to:

a first end sidewall of the upper first fin region; and

a first end sidewall of the upper second fin region; and

communicatively coupling a second S/D region to:

a second end sidewall of the upper first fin region; and

a second end sidewall of the upper second fin region;

wherein the upper first fin region and the upper second fin region function as channel regions of the semiconductor device.