Tuning threshold voltage in field-effect transistors

1. A method, comprising:

forming a gate dielectric layer over an interfacial layer disposed over a semiconductor structure;

applying a first metal-containing precursor over the gate dielectric layer to form a first metal-containing layer;

applying a second metal-containing precursor to form an aluminum-containing layer over the first metal-containing layer, aluminum atoms in the aluminum-containing layer subsequently diffusing through the gate dielectric layer to form a second metal-containing layer at an interface between the gate dielectric layer and the interfacial-layer; and

forming a metal gate stack over the first and the second metal-containing layers.

2. The method of claim 1 , wherein forming the gate dielectric layer includes depositing a hafnium oxide-containing layer.

3. The method of claim 1 , wherein applying the first metal-containing precursor includes applying a metal chloride-containing gas or a metal fluoride-containing gas.

4. The method of claim 3 , wherein the metal chloride-containing gas or the metal fluoride-containing gas includes tantalum, tungsten, titanium, or combinations thereof.

5. The method of claim 1 , wherein forming the second metal-containing layer results in the aluminum atoms of the second metal-containing layer and oxygen atoms of the interfacial layer to form aluminum oxide at the interface between the gate dielectric layer and the interfacial layer.

6. The method of claim 1 , wherein applying the first metal-containing precursor and applying the second metal-containing precursor are implemented in an atomic layer deposition apparatus.

7. The method of claim 1 , further comprising removing a top portion of the first metal-containing layer after applying the second metal-containing precursor and before forming the metal gate stack.

8. A method, comprising:

removing a dummy gate structure to form a gate trench over a semiconductor layer;

forming a high-k gate dielectric layer over an interfacial layer exposed in the gate trench;

depositing a metal-containing precursor over the high-k gate dielectric layer to form a metal-containing layer;

depositing an aluminum-containing precursor over the metal-containing layer, wherein depositing the aluminum-containing precursor forms an aluminum oxide layer at an interface between the high-k gate dielectric layer and the interfacial layer, and wherein the metal-containing precursor includes a metal different from aluminum;

subsequent to depositing the aluminum-containing precursor, removing a portion of the metal-containing layer;

depositing a work-function metal layer over a remaining portion of the metal-containing layer; and

forming a bulk conductive layer over the work-function metal layer, resulting in a metal gate structure.

9. The method of claim 8 , wherein depositing the metal-containing precursor includes:

applying the metal-containing precursor; and

purging the metal-containing precursor after applying the metal-containing precursor.

10. The method of claim 8 , wherein depositing the metal-containing precursor includes depositing a metal halide, and wherein the metal halide includes tantalum, tungsten, titanium, or combinations thereof.

11. The method of claim 8 , wherein depositing the aluminum-containing precursor includes:

applying the aluminum-containing precursor; and

purging the aluminum-containing precursor after applying the aluminum-containing precursor.

12. The method of claim 8 , wherein removing the portion of the metal-containing layer includes applying a wet etchant to the metal-containing layer.

13. The method of claim 8 , wherein the aluminum oxide layer at the interface between the high-k gate dielectric layer and the interfacial layer forms dipole moments with the interfacial layer.

14. The method of claim 13 , wherein the aluminum oxide layer at the interface between the high-k gate dielectric layer and the interfacial layer increases work function of the metal gate structure.

15. A method, comprising:

forming an interfacial layer over a semiconductor fin in a gate trench;

forming a gate dielectric layer over the interfacial layer;

depositing an aluminum-free metal precursor over the gate dielectric layer, resulting in a metal-containing layer;

depositing an aluminum-containing metal precursor over the metal-containing layer, wherein the aluminum-containing metal precursor forms an aluminum oxide layer between the gate dielectric layer and the interfacial layer;

removing a portion of the metal-containing layer, wherein a remaining portion of the metal-containing layer includes aluminum; and

forming a metal gate electrode over the remaining portion of the metal-containing layer.

16. The method of claim 15 , wherein depositing the aluminum-free metal precursor includes depositing a metal halide that includes tantalum, tungsten, titanium, or combinations thereof.

17. The method of claim 15 , wherein the interfacial layer includes oxygen, and wherein depositing the aluminum-containing metal precursor results in aluminum in the aluminum-containing metal precursor to diffuse through the metal-containing layer and the gate dielectric layer, thereby forming the aluminum oxide layer with the oxygen in the interfacial layer.

18. The method of claim 15 , subsequent to depositing the aluminum-containing metal precursor, the method further comprising cyclically depositing of the aluminum-free metal precursor and depositing of the aluminum-containing metal precursor to increase a thickness of the aluminum oxide layer.

19. The method of claim 15 , further comprising:

purging the aluminum-free metal precursor before depositing the aluminum-containing metal precursor; and

purging the aluminum-containing metal precursor before removing the portion of the metal-containing layer.

20. The method of claim 1 , wherein the diffusing results in a concentration of the aluminum atoms to gradually decrease from the first metal-containing layer to the second metal-containing layer.