Method and structure for robust finFET replacement metal gate integration

1. A method of forming a semiconductor structure comprising:

forming at least one sacrificial gate structure over a portion of at least one semiconductor fin formed on a substrate, the at least one sacrificial gate structure comprising a sacrificial gate material and at least one hard mask atop the sacrificial gate material;

forming an interlevel dielectric (ILD) layer over the at least one sacrificial gate structure, the at least one semiconductor fin and the substrate;

recessing the ILD layer to expose the at least one hard mask and a top portion of the sacrificial gate material;

forming a first gate spacer on sidewalls of the at least one hard mask and the top portion of the sacrificial gate material;

removing a remaining portion of the ILD layer to expose a remaining portion of the sacrificial gate material; and

forming a second gate spacer on sidewalls of the remaining portion of the sacrificial gate material.

2. The method of claim 1 , wherein a top surface of the remaining portion of the ILD layer is 20 nm below a top surface of the sacrificial gate material.

3. The method of claim 1 , wherein the first gate spacer comprises a high-k dielectric material selected from the group consisting of hafnium oxide, hafnium silicate, zirconium oxide, zirconium silicate aluminum oxide and tantalum oxide.

4. The method of claim 1 , wherein the second gate spacer comprises a material having a etch resistance lower than a etch resistance of the first gate spacer.

5. The method of claim 4 , wherein the second gate spacer comprises a dielectric nitride selected from the group consisting of silicon nitride, silicon oxynitride, silicon boron nitride and silicon carbon nitride.

6. The method of claim 1 , wherein the second gate spacer is located beneath a corresponding first gate spacer and has width no greater than a width of the corresponding first gate spacer.

7. The method of claim 1 , wherein the ILD layer comprises amorphous carbon or a flowable oxide selected from the group consisting of a polymer hydrogen silsesquioxane (HSQ) and a carbon doped silicon oxide.

8. The method of claim 1 , wherein the at least one hard mask comprises a first hard mask present on the sacrificial gate material and a second hard mask present on the first hard mask.

9. The method of claim 8 , wherein the first hard mask comprises silicon nitride, silicon oxynitride, silicon boron nitride or silicon carbon nitride, and wherein the second hard mask comprises silicon oxide.

10. The method of claim 1 , wherein the forming the first gate spacer comprises:

forming a conformal first gate spacer material layer on exposed surfaces of the at least one sacrificial gate structure and the remaining portion of the ILD layer; and

removing horizontal portions of the conformal first spacer material layer.

11. The method of claim 1 , wherein the forming the second gate spacer comprises:

forming a conformal second gate spacer material layer on exposed surfaces of the at least one sacrificial gate structure, the first gate spacer, the at least one fin structure and the substrate; and

removing portions of the conformal second gate spacer material layer that are not covered by the first gate spacer.

12. The method of claim 1 , further comprising forming an epitaxial source region and an epitaxial drain region on portions of the at least one semiconductor fins that are not covered by the sacrificial gate structure and the second gate spacer.

13. The method of claim 12 , further comprising removing the at least one sacrificial gate structure to provide at least one gate cavity, wherein the removing the at least one sacrificial gate structure comprise:

forming another ILD layer over exposed surfaces of the at least one sacrificial gate structure, the first gate spacer, the epitaxial source region, the epitaxial drain region and the substrate, wherein the another ILD layer has an upper surface coplanar with an upper surface of the sacrificial gate structure;

removing the at least one sacrificial hard mask; and

removing the sacrificial gate material.

14. The method of claim 13 , further comprising forming at least one gate structure in the at least one gate cavity, wherein the forming the at least gate structure comprises:

forming a gate dielectric on sidewalls and a bottom surface of the gate cavity;

forming a gate electrode on the gate dielectric to fill a remaining volume of the gate cavity;

recessing the gate electrode;

recessing the gate dielectric, the gate dielectric having a top surface coplanar with a top surface of the gate electrode; and

forming a gate cap on the top surface of the gate dielectric and the top surface of the gate electrode.

15. The method of claim 14 , wherein the gate cap is in contact with the first gate spacer and has a bottom surface above an interface between the first gate spacer and the second spacer.

16. A semiconductor structure comprising:

at least one fin structure present on a substrate;

at least one gate structure present over a channel portion of the at least one fin structure, the gate structure comprising a U-shaped gate dielectric, a gate electrode present on a bottom and sidewalls of the U-shaped gate dielectric, and a gate cap atop the U-shaped gate dielectric and the gate electrode;

a first gate spacer present on sidewalls of an upper portion of the at least one gate structure, the first gate spacer in contact with an entirety of the gate cap and an upper portion of vertical portions of the U-shaped gate dielectric;

a second gate spacer present underneath the first gate spacer, the second gate spacer in contact with a remaining portion of the vertical portions of the U-shaped gate dielectric; and

an epitaxial source region and an epitaxial drain region on opposite sides of the at least gate structure adjacent the second gate spacer,

wherein the first gate spacer comprises a material having a higher etch resistance than the second gate spacer.

17. The semiconductor structure of claim 16 , wherein the first gate spacer comprises a high-k dielectric material selected from the group consisting of hafnium oxide, hafnium silicate, zirconium oxide, zirconium silicate aluminum oxide and tantalum oxide.

18. The semiconductor structure of claim 16 , wherein the second gate spacer comprises a material having a etch resistance lower than a etch resistance of a material of the first gate spacer.

19. The semiconductor structure of claim 18 , wherein the second gate spacer comprises a dielectric nitride selected from the group consisting of silicon nitride, silicon oxynitride, silicon boron nitride and silicon carbon nitride.

20. The semiconductor structure of claim 16 , wherein the second gate spacer has a width no greater than a width of the first gate spacer.