Dielectric cap structure in semiconductor devices and methods of manufacturing the same

1. A semiconductor device, comprising:

a channel structure;

a first gate structure straddling the channel structure;

an epitaxial structure, adjacent the first gate structure, that is coupled to an end of the channel structure;

a first contact structure disposed over and in contact with the epitaxial structure;

a nitride-based conformal layer extending at least over the first contact structure; and

an oxide-based layer disposed over the nitride-based conformal layer;

wherein a first portion of the nitride-based conformal layer, disposed over the first contact structure, has a dip that is filled with a first portion of the oxide-based layer, and

wherein a second portion of the nitride-based conformal layer, extending continuously from the first portion of the nitride-based conformal layer, is disposed over a top surface of the first gate structure.

2. The semiconductor device of claim 1 , further comprising a second contact structure disposed over the first gate structure, wherein the second contact structure penetrates through a second portion of the oxide-based layer and the second portion of the nitride-based conformal layer to be in contact with the first gate structure.

3. The semiconductor device of claim 2 , further comprising a gate spacer interposed between the first contact structure and the first gate structure, wherein the second contact structure and the nitride-based conformal layer directly contact the first gate spacer.

4. The semiconductor device of claim 2 , further comprising a gate spacer interposed between the first contact structure and the first gate structure, wherein the second contact structure is separated apart from the gate spacer with the nitride-based conformal layer and the second portion of the oxide-based layer.

5. The semiconductor device of claim 2 , further comprising a third contact structure disposed over the first contact structure, wherein the third contact structure penetrates through the first portion of the oxide-based layer and the nitride-based conformal layer to be in contact with the first contact structure.

6. The semiconductor device of claim 5 , further comprising an etch stop layer disposed over the oxide-based layer and the nitride-based conformal layer, wherein the second and third contact structures further penetrate through the etch stop layer, respectively.

7. The semiconductor device of claim 6 , wherein the etch stop layer has a top surface and a bottom surface, and wherein a portion of the top surface and a portion of the bottom surface that are disposed above a second gate structure each have a dip.

8. The semiconductor device of claim 1 , wherein the channel structure includes a plurality of nanostructures vertically spaced apart from one another.

9. The semiconductor device of claim 8 , wherein the first gate structure wraps around each of the plurality of nanostructures.

10. The semiconductor device of claim 1 , wherein the channel structure contains a fin structure that is integrally formed from a substrate.

11. A semiconductor device, comprising:

a channel structure;

a first gate structure straddling the channel structure;

a source/drain structure, adjacent the first gate structure, that is coupled to an end of the channel structure;

a first contact structure disposed over and in contact with the source/drain structure;

a gate spacer disposed between the first gate structure and the first contact structure;

a nitride-based conformal layer extending over the first contact structure, the gate spacer, and at least a portion of the first gate structure;

an oxide-based layer disposed over the nitride-based conformal layer; and

a second contact structure that penetrates through a first portion of the oxide-based layer and the nitride-based conformal layer to be in contact with the first gate structure, wherein the first portion of the oxide-based layer extends to below a top surface the nitride-based conformal layer.

12. The semiconductor device of claim 11 , wherein a portion of the nitride-based conformal layer, disposed over the first contact structure, has a dip that is filled with a second portion of the oxide-based layer.

13. The semiconductor device of claim 11 , further comprising an etch stop layer disposed over the oxide-based layer and the nitride-based conformal layer, wherein the second contact structure further penetrates through the etch stop layer.

14. The semiconductor device of claim 13 , wherein the etch stop layer has a top surface and a bottom surface, and wherein a portion of the top surface and a portion of the bottom surface that are disposed above a second gate structure each have a dip.

15. The semiconductor device of claim 14 , wherein the nitride-based conformal layer also extends over the second gate structure.

16. The semiconductor device of claim 11 , wherein the channel structure includes a plurality of nanostructures vertically spaced apart from one another.

17. The semiconductor device of claim 16 , wherein the first gate structure wraps around each of the plurality of nanostructures.

18. A method for making semiconductor devices, comprising:

forming a semiconductor device that at least includes a gate structure straddling a channel structure and a first epitaxial structure adjacent the gate structure, wherein the first epitaxial structure is overlaid by an interlayer dielectric;

forming a nitride-based conformal layer that extends over the gate structure and the interlayer dielectric;

forming an oxide-based layer over the nitride-based conformal layer, wherein the oxide-based layer includes a first portion that fills up a recess above the gate structure; and

forming a first contact structure that extends through the first portion of the oxide-based layer and the nitride-based conformal layer to couple to the gate structure.

19. The method of claim 18 , further comprising forming an etch stop layer over the oxide-based layer, wherein the first contact structure further extends through the etch stop layer.

20. The method of claim 18 , wherein the semiconductor device further includes a second epitaxial structure opposite the gate structure from the first epitaxial structure, the method further comprises:

prior to the step of forming the nitride-based conformal layer, forming a second contact structure coupled to the second epitaxial structure, wherein a portion of nitride-based layer, disposed over the second contact structure, has a dip that is filled with a second portion of the oxide-based layer.