Nanosheet field-effect transistor device and method of forming

1. A semiconductor device comprising:

a first fin protruding above a substrate, wherein the first fin is in an N-type device region of the semiconductor device;

a second fin protruding above the substrate, wherein the second fin is in a P-type device region of the semiconductor device;

first source/drain regions over the first fin;

second source/drain regions over the second fin;

first nanosheets between the first source/drain regions;

second nanosheets between the second source/drain regions;

a first gate layer stack around the first nanosheets, wherein the first gate layer stack fills first spaces between adjacent first nanosheets, wherein the first gate layer stack has a first number of sublayers at a first location between adjacent first nanosheets, and has a second number of sublayers at a second location over a topmost first nanosheet distal from the substrate, the first number being larger than the second number, wherein the first gate layer stack has a first thickness between adjacent first nanosheets, wherein the first thickness is equal to a distance between adjacent first nanosheets; and

a second gate layer stack around the second nanosheets, wherein the second gate layer stack fills second spaces between adjacent second nanosheets, wherein the second gate layer stack has a third number of sublayers at a third location between adjacent second nanosheets, and has a fourth number of sublayers at a fourth location over a topmost second nanosheet distal from the substrate, the third number being larger than the fourth number, wherein the first number is different from the third number, and the second number is different from the fourth number.

2. The semiconductor device of claim 1 , wherein the first number is larger than the third number, and the second number is larger than the fourth number.

3. The semiconductor device of claim 1 , wherein the first gate layer stack has a second thickness over the topmost first nanosheet, wherein the second thickness is different from the first thickness.

4. The semiconductor device of claim 3 , wherein the second thickness is about half of the first thickness.

5. The semiconductor device of claim 1 , wherein the first gate layer stack comprises a sublayer of a gate dielectric material, a sublayer of a first liner material, a sublayer of a first work function material, and a sublayer of a second liner material.

6. The semiconductor device of claim 5 , wherein the second liner material is the same as the first liner material.

7. The semiconductor device of claim 5 , wherein the gate dielectric material surrounds the first nanosheets, the first liner material contacts and surrounds the gate dielectric material, the first work function material contacts and surrounds the first liner material, and the second liner material contacts and surrounds the first work function material.

8. The semiconductor device of claim 5 , wherein the second gate layer stack comprises a sublayer of the gate dielectric material and a sublayer of a second work function material.

9. The semiconductor device of claim 8 , wherein the first work function material is an n-type work function material, and the second work function material is a p-type work function material.

10. The semiconductor device of claim 8 , wherein the gate dielectric material surrounds the second nanosheets, and the second work function material contacts and surrounds the gate dielectric material.

11. A semiconductor device comprising:

a fin protruding above a substrate;

source/drain regions over the fin;

nanosheets between the source/drain regions;

a gate layer stack around the nanosheets, wherein the gate layer stack fills spaces between adjacent nanosheets, wherein the gate layer stack comprises a sublayer of a gate dielectric material, a sublayer of a first liner material, a sublayer of a work function material, and a sublayer of a second liner material, wherein the gate layer stack has a first thickness at a first location between adjacent nanosheets, and has a second thickness at a second location over a topmost nanosheet distal from the substrate, the second thickness being smaller than the first thickness; and

a gate electrode material around the gate layer stack, wherein there is no gate electrode material between adjacent nanosheets.

12. The semiconductor device of claim 11 , wherein the gate layer stack has a first number of sublayers at the first location, and has a second number of sublayers at the second location, the first number being larger than the second number.

13. The semiconductor device of claim 11 , wherein the second thickness is about half of the first thickness.

14. The semiconductor device of claim 11 , wherein the first liner material is the same as the second liner material.

15. The semiconductor device of claim 14 , wherein the work function material is titanium aluminum carbide, wherein the second liner material and the first liner material are titanium nitride.

16. The semiconductor device of claim 11 , wherein the nanosheets comprise a first nanosheet and a second nanosheet adjacent to the first nanosheet, wherein the second nanosheet is between the first nanosheet and the substrate, wherein the gate layer stack extends continuously from a lower surface of the first nanosheet facing the substrate to an upper surface of the second nanosheet distal from the substrate.

17. A method of forming a semiconductor device, the method comprising:

forming first nanosheets over a first fin in an N-type device region of the semiconductor device;

forming second nanosheets over a second fin in a P-type device region of the semiconductor device;

forming a first gate layer stack and a second gate layer stack around the first nanosheets and the second nanosheets, respectively, wherein the first gate layer stack and the second gate layer stack have a same structure that includes a gate dielectric layer, a first liner layer, a first work function layer, and a second liner layer, wherein the first gate layer stack fills first spaces between adjacent first nanosheets, and the second gate layer stack fills second spaces between adjacent second nanosheets;

after forming the first gate layer stack and the second gate layer stack, removing the second liner layer, the first work function layer, and the first liner layer of the second gate layer stack to form gaps between adjacent second nanosheets; and

after the removing, forming a second work function layer around the gate dielectric layer of the second gate layer stack, wherein the second work function layer fills the gaps between the adjacent second nanosheets.

18. The method of claim 17 , wherein forming the first gate layer stack comprises:

forming the gate dielectric layer around the first nanosheets;

forming the first liner layer around the gate dielectric layer;

forming the first work function layer around the first liner layer; and

forming the second liner layer around the first work function layer.

19. The method of claim 18 , wherein the first liner layer and the second liner layer are formed of a same material.

20. The method of claim 18 , wherein the first work function layer is formed of an n-type work function material, and the second work function layer is formed of a p-type work function material.