Semiconductor device and manufacturing method thereof

1. A method, comprising:

removing a dummy gate structure to form a trench between a pair of spacers, in which a semiconductor fin is exposed;

forming a self-assembling monolayer on inner sidewalls of the spacers, the self-assembling monolayer having a hydrophobic surface;

forming an interfacial layer on the exposed semiconductor fin, the interfacial layer having a hydrophilic surface;

depositing a high-k dielectric layer in the trench, wherein a first portion of the high-k dielectric layer on the hydrophilic surface of the interfacial layer is thicker than a second portion of the high-k dielectric layer on the hydrophobic surface of the self-assembling monolayer; and

removing the second portion of the high-k dielectric layer, while leaving the first portion of the high-k dielectric layer on the interfacial layer.

2. The method of claim 1 , wherein the removing the second portion of the high-k dielectric layer reduces a thickness of the first portion of the high-k dielectric layer on the interfacial layer.

3. The method of claim 1 , further comprising removing the self-assembling monolayer to form gaps on either side of the first portion of the high-k dielectric layer.

4. The method of claim 3 , wherein the self-assembling monolayer is removed after the second portion of the high-k dielectric layer is removed.

5. The method of claim 3 , wherein the interfacial layer is separated from the spacers by the gaps.

6. The method of claim 3 , further comprising forming a metal gate structure over the first portion of the high-k dielectric layer and in the gap.

7. The method of claim 1 , wherein the high-k dielectric layer is deposited at a faster deposition rate on the hydrophilic surface of the interfacial layer than on the hydrophobic surface of the self-assembling monolayer.

8. The method of claim 1 , wherein the inner sidewalls of the spacers are hydrophilic, an exposed surface of the semiconductor fin is hydrophobic, and the self-assembling monolayer is selectively formed on the hydrophilic inner sidewalls of the spacers and not on the hydrophobic surface of the semiconductor fin.

9. The method claim 1 , wherein the interfacial layer is formed using wet oxidation, and the hydrophobic surface of the self-assembling monolayer remains exposed after the wet oxidation is complete.

10. A semiconductor device, comprising:

a fin structure over a substrate;

a metal gate structure extending across the fin structure;

source and drain regions respectively on opposite sides of the metal gate structure;

first and second spacers on opposite sidewalls of the metal gate structure, respectively; and

a high-k dielectric layer between the metal gate structure and the fin structure, wherein in a cross-sectional view along a plane containing cross-sections of the source and drain regions, the metal gate structure has a first portion laterally spacing the high-k dielectric layer apart from the first spacer.

11. The semiconductor device of claim 10 , wherein the first portion of the metal gate structure has a width in a range from about 0.5 nm to about 30 nm.

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

an interfacial layer between the high-k dielectric layer and the fin structure, wherein the first portion of the metal gate structure is further laterally between the interfacial layer and the first spacer.

13. The semiconductor device of claim 12 , wherein the metal gate structure has a second portion laterally between the interfacial layer and the second spacer.

14. The semiconductor device of claim 10 , wherein the metal gate structure has a second portion laterally between the high-k dielectric layer and the second spacer.

15. The semiconductor device of claim 14 , wherein the second portion of the metal gate structure has a width in a range from about 0.5 nm to about 30 nm.

16. The semiconductor device of claim 10 , wherein the first portion of the metal gate structure is in contact with the fin structure.

17. A method of manufacturing a semiconductor device, comprising:

forming a fin structure comprising alternately stacked first semiconductor layers and second semiconductor layers over a substrate;

forming a sacrificial gate structure over the fin structure;

forming spacers on either side of the sacrificial gate structure;

removing the sacrificial gate structure to form a trench between the spacers;

removing the first semiconductor layers from the trench, while leaving the second semiconductor layers suspended in the trench;

forming a self-assembling monolayer on sidewalls of the spacers in the trench;

forming interfacial layers encircling the suspended second semiconductor layers, respectively;

depositing a high-k dielectric layer at a faster deposition rate on the interfacial layers than on the self-assembling monolayer; and

forming a metal gate structure over the high-k dielectric layer.

18. The method of claim 17 , further comprising:

prior to forming the metal gate structure, removing the self-assembling monolayer from above a topmost one of the second semiconductor layers.

19. The method of claim 17 , further comprising:

after forming the spacers and before removing the sacrificial gate structure, laterally recessing the first semiconductor layers with respect to the second semiconductor layers;

forming inner spacers on either side of the laterally recessed first semiconductor layers; and

forming a source epitaxial structure and a drain epitaxial structure adjacent to the inner spacers, respectively.

20. The method of claim 19 , wherein the self-assembling monolayer is further formed on the inner spacers.