Gate structure in semiconductor device and method of forming the same

1. A method comprising:

removing a first dummy gate stack and a second dummy gate stack to form a first trench and a second trench, wherein the first dummy gate stack and the second dummy gate stack are in a first device region and a second device region, respectively;

depositing a first gate dielectric layer and a second gate dielectric layer extending into the first trench and the second trench, respectively;

forming a fluorine-containing layer comprising a first portion over the first gate dielectric layer, and a second portion over the second gate dielectric layer;

removing the second portion of the fluorine-containing layer;

performing an annealing process to diffuse fluorine in the first portion of the fluorine-containing layer into the first gate dielectric layer; and

after the annealing process, forming a first work-function layer and a second work-function layer over the first gate dielectric layer and the second gate dielectric layer, respectively.

2. The method of claim 1 , wherein the forming the fluorine-containing layer comprises depositing the fluorine-containing layer using a fluorine-containing precursor.

3. The method of claim 2 , wherein the fluorine-containing precursor comprises WF 6 .

4. The method of claim 3 , wherein the depositing the fluorine-containing layer is performed using an additional precursor comprising silane.

5. The method of claim 1 , wherein the forming the fluorine-containing layer comprises soaking a corresponding wafer comprising the first gate dielectric layer and the second gate dielectric layer in a fluorine-containing process gas.

6. The method of claim 5 , wherein the soaking results in a surface portion of the first gate dielectric layer in contact with the fluorine-containing process gas to have an increased fluorine atomic percentage and to form the fluorine-containing layer.

7. The method of claim 5 , wherein the fluorine-containing process gas is selected from NF 3 , WF 6 , or combinations thereof.

8. The method of claim 1 further comprising:

before the forming the fluorine-containing layer, depositing a protection layer comprising a first part and a second part on the first gate dielectric layer and the second gate dielectric layer, respectively.

9. The method of claim 8 , wherein in the removing the second portion of the fluorine-containing layer, a portion of the protection layer is further removed from over the second gate dielectric layer.

10. The method of claim 9 further comprising, after the annealing process, removing an additional portion of the protection layer from over the first gate dielectric layer.

11. The method of claim 1 further comprising forming a first source/drain region on a side of the first work-function layer and a second source/drain region on a side of the second work-function layer, wherein the first source/drain region and the second source/drain region are of opposite conductivity types.

12. The method of claim 1 further comprising forming a first source/drain region on a side of the first work-function layer and a second source/drain region on a side of the second work-function layer, wherein the first source/drain region and the second source/drain region are of a same conductivity type.

13. The method of claim 1 , wherein the first dummy gate stack is formed on a top surface and sidewalls of a multilayer stack, and wherein the multilayer stack comprises a plurality of sacrificial layers and a plurality of nanostructures provided alternatingly.

14. A method comprising:

forming a first dummy gate stack on a top surface and sidewalls of a first multilayer stack, wherein the first multilayer stack comprises a first plurality of sacrificial layers and a first plurality of nanostructures provided alternatingly;

forming a second dummy gate stack on a top surface and sidewalls of a second multilayer stack, wherein the second multilayer stack comprises a second plurality of sacrificial layers and a second plurality of nanostructures provided alternatingly;

removing the first dummy gate stack and the second dummy gate stack to form a first recess and a second recess, respectively, in a dielectric layer;

removing the first plurality of sacrificial layers and the second plurality of sacrificial layers;

depositing first gate dielectrics wrapping around the first plurality of nanostructures;

depositing second gate dielectrics wrapping around the second plurality of nanostructures;

depositing first protection layers and second protection layers on the first gate dielectrics and the second gate dielectrics, respectively;

forming first fluorine-containing layers and second fluorine-containing layers on the first protection layers and the second protection layers, respectively;

removing the second fluorine-containing layers;

after the second fluorine-containing layers are removed, performing an annealing process, wherein the first fluorine-containing layers are subject to the annealing process; and

after the annealing process, removing the first fluorine-containing layers.

15. The method of claim 14 further comprising:

removing the first protection layers and the second protection layers; and

forming work-function layers in spaces left by the removed first protection layers and the removed second protection layers.

16. The method of claim 14 further comprising forming a first work-function layer and a second work-function layer on the first protection layers and the second gate dielectrics, respectively.

17. The method of claim 14 , wherein the forming the first fluorine-containing layers and the second fluorine-containing layers comprises a deposition process or a soaking process.

18. A method comprising:

forming a first nano structure in a first trench, with a first gate spacer comprising portions on opposite sides of the first trench;

forming a second nanostructure in a second trench, with a second gate spacer comprising portions on opposite sides of the second trench;

depositing a first gate dielectric extending into the first trench to encircle the first nanostructure;

depositing a second gate dielectric extending into the second trench to encircle the second nanostructure; and

after the first gate dielectric and the second gate dielectric are formed, adding fluorine into the first gate dielectric, wherein when the fluorine is added into the first gate dielectric, fluorine remains substantially unchanged in the second gate dielectric.

19. The method of claim 18 , wherein the adding the fluorine comprises:

forming a fluorine-containing layer on the first gate dielectric; and

performing an annealing process to drive the fluorine in the fluorine-containing layer into the first gate dielectric.

20. The method of claim 19 , wherein the fluorine-containing layer is further formed to extend on the second gate dielectric, and the method further comprising, before the annealing process, removing the fluorine-containing layer from the second trench.