Gate structures in transistors and method of forming same

1. A device comprising:

a first nanostructure;

a second nanostructure over the first nanostructure;

a first high-k gate dielectric around the first nanostructure;

a second high-k gate dielectric around the second nanostructure, wherein the first high-k gate dielectric and the second high-k gate dielectric each comprise fluorine; and

a gate electrode over the first and second high-k gate dielectrics, wherein the gate electrode comprises:

a first work function metal;

a second work function metal over the first work function metal; and

a first metal residue at an interface between the first work function metal and the second work function metal, wherein the first metal residue has a metal element that is different than a metal element of the first work function metal.

2. The device of claim 1 , wherein the first high-k gate dielectric further comprises hafnium oxide, and wherein a ratio of fluorine to hafnium in the first high-k gate dielectric is in a range of 0.015 to 0.2.

3. The device of claim 2 , wherein a ratio of the metal element of the first metal residue to hafnium in a region between the first nanostructure and the second nanostructure is less than 0.1.

4. The device of claim 1 , wherein the metal element of the first metal residue is tungsten.

5. The device of claim 1 , wherein the gate electrode further comprises a second metal residue at the interface between the first work function metal and the second work function metal, wherein the second metal residue has a same metal element as the first metal residue, and wherein the second metal residue is disconnected from the first metal residue.

6. The device of claim 1 , wherein the metal element of the first metal residue is different than a metal element of the second work function metal.

7. The device of claim 1 , wherein the gate electrode further comprises:

an adhesion layer over the second work function metal; and

a fill metal over the adhesion layer.

8. The device of claim 1 , wherein the first metal residue is further disposed at a second interface between the first work function metal and the second work function metal, wherein the second work function metal extends continuously from the interface to the second interface.

9. A transistor comprising:

a first nanostructure over a semiconductor substrate;

a second nanostructure over the first nanostructure;

a gate dielectric surrounding the first nanostructure and the second nanostructure, wherein the gate dielectric comprises hafnium and fluorine, and wherein a ratio of fluorine to hafnium in the gate dielectric is in a range of 0.015 and 0.2; and

a gate electrode over the gate dielectric, wherein the gate electrode comprises:

a first p-type work function metal;

a second p-type work function metal over the first p-type work function metal;

an adhesion layer over the second p-type work function metal; and

a fill metal over the adhesion layer, wherein the fill metal does not extend between the first nanostructure and the second nanostructure.

10. The transistor of claim 9 , further comprising a metal residue at an interface between the first p-type work function metal and the second p-type work function metal.

11. The transistor of claim 10 , wherein the metal residue is tungsten.

12. The transistor of claim 9 , wherein the first p-type work function metal comprises fluorine, and wherein the second p-type work function metal has a lower concentration of fluorine than the first p-type work function metal.

13. A method comprising:

depositing a gate dielectric around a first nanostructure and a second nanostructure, the first nanostructure is disposed over the second nanostructure;

depositing a first p-type work function metal over the gate dielectric, the first p-type work function metal is disposed around the first nanostructure and the second nanostructure;

performing a fluorine treatment on the first p-type work function metal, wherein the fluorine treatment is a deposition process that exposes a surface of the first p-type work function metal to a fluorine-containing precursor, and wherein the fluorine treatment does not use a chemical that triggers a reduction-oxidation reaction with the fluorine-containing precursor; and

after performing the fluorine treatment, depositing a second p-type work function metal over the first p-type work function metal.

14. The method of claim 13 , wherein the fluorine-containing precursor is WF x , NF x , TiF x , TaF x , or HfF x , and wherein x is an integer in a range of 1 to 6.

15. The method of claim 14 , wherein the fluorine treatment forms a metal residue on the first p-type work function metal.

16. The method of claim 15 , wherein the metal residue is tungsten residue, wherein the gate dielectric comprises hafnium, and wherein after performing the fluorine treatment, a ratio of tungsten to hafnium in a region between the first nanostructure and the second nanostructure is less than 0.1.

17. The method of claim 13 , wherein the fluorine treatment is performed at a temperature in a range of 250° C. to 475° C.

18. The method of claim 13 , wherein the fluorine treatment is performed for a duration of 1 second to 15 minutes.

19. The method of claim 13 , wherein the fluorine treatment comprises diffusing fluorine into the gate dielectric.

20. The method of claim 13 , wherein the gate dielectric comprises hafnium, and wherein after performing the fluorine treatment, a ratio of fluorine to hafnium in the gate dielectric is in a range of 0.015 and 0.2.