Gate air spacer for fin-like field effect transistor

1. A transistor comprising:

a fin; and

a gate structure disposed over the fin between a first epitaxial source/drain feature and a second epitaxial source/drain feature, wherein the gate structure includes:

a gate electrode,

a gate dielectric, and

gate air spacers disposed between the gate dielectric and sidewalls of the gate electrode.

2. The transistor of claim 1 , wherein the gate structure is free of gate dielectric spacers along sidewalls of the gate electrode.

3. The transistor of claim 1 , wherein the gate air spacers are disposed between the gate dielectric and a first portion of the sidewalls of the gate electrode, the transistor further comprising a gate air spacer seal disposed between the gate dielectric and a second portion of the sidewalls of the gate electrode, wherein the second portion of the sidewalls of the gate electrode is disposed over the first portion of the sidewalls of the gate electrode.

4. The transistor of claim 3 , wherein the gate air spacer seal is further disposed over a top surface of the gate electrode.

5. The transistor of claim 3 , further comprising a gate contact that extends through the gate air spacer seal to the gate electrode.

6. The transistor of claim 1 , wherein a top surface of the gate dielectric is higher than a top surface of the gate electrode relative to a top surface of the fin.

7. The transistor of claim 1 , further comprising a dielectric layer disposed over the fin, the first epitaxial source/drain feature, and the second epitaxial source/drain feature, wherein the dielectric layer physically contacts sidewalls of the gate dielectric.

8. The transistor of claim 7 , wherein the dielectric layer includes an interlevel dielectric layer disposed over a contact etch stop layer.

9. The transistor of claim 8 , wherein a first portion of the contact etch stop layer is disposed between and physically contacts the gate dielectric and the first epitaxial source/drain feature and a second portion of the contact etch stop layer is disposed between and physically contacts the gate dielectric and the second epitaxial source/drain feature.

10. A transistor comprising:

a fin;

a first epitaxial source/drain feature disposed in a first source/drain region of the fin and a second epitaxial source/drain feature disposed in a second source/drain region of the fin;

a gate structure disposed over the fin between the first epitaxial source/drain feature and the second epitaxial source/drain feature, wherein the gate structure includes:

a gate electrode,

a gate dielectric,

a gate air spacer seal,

a first gate air spacer confined between the gate dielectric, a first sidewall of the gate electrode, and the gate air spacer seal, and

a second gate air spacer confined between the gate dielectric, a second sidewall of the gate electrode, and the gate air spacer seal; and

a gate contact that extends through the gate air spacer seal to the gate electrode.

11. The transistor of claim 10 , wherein:

a first edge and a second edge of the gate structure are defined by the gate dielectric;

the first edge is substantially, vertically aligned with a first source/drain tip of the first epitaxial source/drain feature; and

the second edge is substantially, vertically aligned with a second source/drain tip of the first epitaxial source/drain feature.

12. The transistor of claim 10 , wherein:

the first gate air spacer and the second gate air spacer have a first thickness;

the gate electrode has a second thickness; and

the first thickness is less than the second thickness, such that the first gate air spacer is disposed along a portion of the first sidewall of the gate electrode and the second gate air spacer is disposed along a portion of the second sidewall of the gate electrode.

13. The transistor of claim 12 , wherein

the portion of the first sidewall of the gate electrode is a lower portion of the first sidewall of the gate electrode and the portion of the second sidewall of the gate electrode is a lower portion of the second sidewall of the gate electrode; and

the gate air spacer seal is disposed between and separates an upper portion of the first sidewall of the gate electrode and an upper portion of the second sidewall of the gate electrode.

14. The transistor of claim 10 , wherein:

the first gate air spacer and the second gate air spacer have a first thickness;

the gate electrode has a second thickness; and

the first thickness is substantially equal to the second thickness, such that the first gate air spacer is disposed along an entirety of the first sidewall of the gate electrode and the second gate air spacer is disposed along an entirety of the second sidewall of the gate electrode.

15. The transistor of claim 10 , further comprising a dielectric layer of a multilayer interconnect feature disposed over the fin, the first epitaxial source/drain feature, the second epitaxial source/drain feature, and the gate structure, wherein the dielectric layer is disposed between and physically contacts the first epitaxial source/drain feature and the gate dielectric and the dielectric layer is further disposed between and physically contacts the second epitaxial source/drain feature and the gate dielectric.

16. A method comprising:

after forming a first epitaxial source/drain feature and a second epitaxial source/drain feature, removing gate spacers from along sidewalls of a dummy gate stack disposed over a fin between the first epitaxial source/drain feature and the second epitaxial source/drain feature;

replacing the dummy gate stack with a metal gate stack, wherein the metal gate stack includes a gate electrode disposed over a gate dielectric and a dummy spacer disposed between the gate dielectric and sidewalls of the gate electrode;

removing the dummy spacer from the metal gate stack to form a gate air spacer in the metal gate stack between the gate dielectric and the sidewalls of the gate electrode; and

forming a gate air spacer seal over the gate air spacer.

17. The method of claim 16 , wherein the replacing the dummy gate stack with the metal gate stack includes:

removing the dummy gate stack from a dielectric layer to form a gate opening defined in the dielectric layer that exposes the fin;

forming a gate dielectric layer that partially fills the gate opening, wherein the gate dielectric layer is disposed over the dielectric layer and the fin;

forming a dummy spacer layer that partially fills the gate opening, wherein the dummy spacer layer is disposed over the gate dielectric layer;

forming a gate electrode layer that fills a remaining portion of the gate opening, wherein the gate electrode layer is disposed over the dummy spacer layer; and

performing a planarization process on the gate electrode layer, the dummy spacer layer, and the gate dielectric layer.

18. The method of claim 17 , wherein the forming the dummy spacer layer includes:

depositing the dummy spacer layer over the gate dielectric layer, such that the dummy spacer layer is disposed over sidewalls of the gate opening defined by the dielectric layer and over a bottom of the gate opening defined by the fin;

forming a passivation layer over the dummy spacer layer disposed over the sidewalls of the gate opening defined by the dielectric layer;

removing the dummy spacer layer disposed over the bottom of the gate opening defined by the fin to expose a portion of the gate dielectric layer that is disposed over the bottom of the gate opening defined by the fin; and

removing the passivation layer.

19. The method of claim 18 , wherein:

the forming the passivation layer and the removing the dummy spacer layer includes performing a dry etch process; and

the removing the passivation layer includes performing a wet etch process.

20. The method of claim 16 , further comprising etching back the gate electrode before removing the dummy spacer from the metal gate stack to form the gate air spacer.