Semiconductor device and method for manufacturing the same

1. A semiconductor device, comprising:

an n-channel;

a p-channel;

a first gate dielectric layer around the n-channel;

a first dielectric sheath layer around the first gate dielectric layer;

a second gate dielectric layer around the p-channel;

a second dielectric sheath layer around the second gate dielectric layer, wherein the first dielectric sheath layer and the second dielectric sheath layer comprise different materials; and

a metal gate electrode around the first dielectric sheath layer and the second dielectric sheath layer.

2. The semiconductor device of claim 1 , wherein the first gate dielectric layer and the second gate dielectric layer are made of the same high-k dielectric material.

3. The semiconductor device of claim 1 , wherein the first dielectric sheath layer comprises yttrium oxide (Y 2 O 3 ), lutetium(III) oxide (Lu 2 O 3 ), lanthanum oxide (La 2 O 3 ), strontium oxide (SrO), erbium (Er), scandium (Sc), or combinations thereof.

4. The semiconductor device of claim 1 , wherein the second dielectric sheath layer comprises aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ), magnesium oxide (MgO), or combinations thereof.

5. The semiconductor device of claim 1 , wherein the metal gate electrode continuously extends across the n-channel and the p-channel.

6. The semiconductor device of claim 5 , wherein the metal gate electrode is in contact with the first dielectric sheath layer and the second dielectric sheath layer.

7. The semiconductor device of claim 1 , wherein the metal gate electrode has a first portion in contact with the first dielectric sheath layer and a second portion in contact with the second dielectric sheath layer, and the first portion and the second portion of the metal gate electrode are made of the same material.

8. A semiconductor device, comprising:

a first channel;

a second channel;

a first dielectric sheath layer around the first channel;

a second dielectric sheath layer around the second channel, wherein the first dielectric sheath layer and the second dielectric sheath layer comprise different materials; and

a metal gate electrode continuously extending across the first dielectric sheath layer and the second dielectric sheath layer.

9. The semiconductor device of claim 8 , further comprising:

a first source/drain structure adjoining the first channel;

a second source/drain structure adjoining the second channel; and

an inter-layer dielectric (ILD) layer interposed between the first source/drain structure and the second source/drain structure.

10. The semiconductor device of claim 9 , further comprising:

a first contact over the first source/drain structure; and

a second contact over the second source/drain structure, wherein the ILD layer is further interposed between the first contact and the second contact.

11. The semiconductor device of claim 9 , wherein the first source/drain structure comprises an n-type dopant, and the second source/drain structure comprises a p-type dopant.

12. The semiconductor device of claim 8 , wherein a portion of the first dielectric sheath layer is under a bottom surface of the metal gate electrode.

13. The semiconductor device of claim 8 , further comprising:

a first gate dielectric layer between the first dielectric sheath layer and the first channel; and

a second gate dielectric layer between the second dielectric sheath layer and the second channel, wherein the first gate dielectric layer and the second gate dielectric layer are made of the same high-k dielectric material.

14. A method, comprising:

forming a first nanowire and a second nanowire over a semiconductor substrate;

depositing a first dielectric sheath layer over the first nanowire and the second nanowire;

removing a first portion of the first dielectric sheath layer from the second nanowire, wherein a second portion of the first dielectric sheath layer remains over the first nanowire;

depositing a second dielectric sheath layer over the second nanowire, wherein the first dielectric sheath layer and the second dielectric sheath layer comprise different materials; and

depositing a metal layer over the first dielectric sheath layer and the second dielectric sheath layer.

15. The method of claim 14 , wherein depositing the metal layer is performed such that the metal layer is over and in contact with the first dielectric sheath layer and the second dielectric sheath layer.

16. The method of claim 15 , further comprising:

polishing the metal layer, such that a top surface of the polished metal layer is substantially flat.

17. The method of claim 14 , wherein forming the first nanowire and the second nanowire comprises forming a third nanowire over the first nanowire; and

wherein depositing the first dielectric sheath layer is performed such that the first dielectric sheath layer has the second portion around the first nanowire and a third portion around the third nanowire and such that the second portion and the third portion of the first dielectric sheath layer are merged together.

18. The method of claim 14 , wherein forming the first nanowire and the second nanowire comprises forming a third nanowire over the first nanowire; and

wherein depositing the first dielectric sheath layer is performed such that the first dielectric sheath layer has the second portion around the first nanowire and a third portion around the third nanowire and such that the second portion of the first dielectric sheath layer is spaced from the third portion of the first dielectric sheath layer.

19. The method of claim 14 , wherein forming the first nanowire and the second nanowire comprises forming a third nanowire over the second nanowire; and

wherein depositing the second dielectric sheath layer is performed such that the second dielectric sheath layer has a first portion around the second nanowire and a second portion around the third nanowire and such that the first portion and the second portion of the second dielectric sheath layer are merged together.

20. The method of claim 14 , wherein forming the first nanowire and the second nanowire comprises forming a third nanowire over the second nanowire; and

wherein depositing the second dielectric sheath layer is performed such that the second dielectric sheath layer has a first portion around the second nanowire and a second portion around the third nanowire and such that the first portion of the second dielectric sheath layer is spaced from the second portion of the second dielectric sheath layer.