Semiconductor device having a metal gate and formation method thereof

1. A semiconductor device, comprising:

a substrate having first and second fins extending along a first direction;

an isolation structure over the substrate;

a plurality of gate structures over a plurality of first portions of the first and second fins respectively, wherein the gate structures extend along a second direction perpendicular to the first direction;

source/drain features over a plurality of second portions of the first and second fins respectively;

a dielectric feature over the substrate and not overlapping the first and second fins, wherein a top surface of the dielectric feature is higher than a top surface of the first and second fins and the dielectric feature includes a sidewall that has a first portion directly opposing a first source/drain feature of the source/drain features in the second direction; and

a helmet layer including a plurality of portions, a first portion of the plurality of portions of the helmet layer having a first sub-portion along the first portion of the sidewall of the dielectric feature such that the first sub-portion is directly between the dielectric feature and the first source/drain feature and further having a second sub-portion under a bottom surface of the dielectric feature and directly between the dielectric feature and the isolation structure, wherein the first portion of the helmet layer is a single piece of continuous material.

2. The semiconductor device of claim 1 , wherein the dielectric feature separates one of the gate structures from another of the gate structures.

3. The semiconductor device of claim 1 ,

wherein the first portion of the helmet layer separates the source/drain features from the dielectric feature.

4. The semiconductor device of claim 3 , further comprising:

an interlayer dielectric layer that separates the source/drain features from the helmet layer.

5. The semiconductor device of claim 1 , further comprising:

an interlayer dielectric layer between the first portion of the helmet layer and said at least one of the second portions of the first and second fins, wherein the first portion of the helmet layer separates the interlayer dielectric layer from the dielectric feature.

6. The semiconductor device of claim 1 ,

wherein the gate structures and the dielectric feature are over the isolation structure.

7. The semiconductor device of claim 1 , wherein the second sub-portion of the first portion of the helmet layer is connected to the isolation structure.

8. A semiconductor device, comprising:

a substrate having first and second fins;

a first gate structure over the first fin and having a first gate metal;

a gate spacer extending along sidewalls of the first gate structure;

a second gate structure over the second fin and having a second gate metal;

a dielectric feature over the substrate and not overlapping the first and second fins, wherein the dielectric feature has a first dielectric portion between the first and second gate structures and a second dielectric portion connected with the first dielectric portion, wherein the first dielectric portion of the dielectric feature is in contact with the first and second gate metals of the first and second gate structures, the first and second dielectric portions of the dielectric feature are in direct contact, and the dielectric feature extends beyond an entire width of a combination of the first gate structure and the gate spacer; and

a helmet layer surrounding the second dielectric portion of the dielectric feature.

9. The semiconductor device of claim 8 , wherein the helmet layer terminates before reaching the first dielectric portion.

10. The semiconductor device of claim 8 , wherein the first dielectric portion and the second dielectric portion are connected along a direction that the first and second fins extend along.

11. The semiconductor device of claim 8 , wherein a top surface of the dielectric feature is substantially coplanar with a top surface of the first gate structure.

12. The semiconductor device of claim 8 , wherein a top end of the helmet layer is substantially coplanar with a top surface of the dielectric feature.

13. The semiconductor device of claim 8 , wherein the first dielectric portion is connected with the first and second gate structures and the helmet layer is between the second dielectric portion and at least one of the first and second fins.

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

an isolation structure between the first and second fins, wherein the first and second gate structures and the dielectric feature are over the isolation structure, the first dielectric portion is connected with the isolation structure, and the helmet layer is between the second dielectric portion and the isolation structure.

15. The semiconductor device of claim 8 , wherein the helmet layer is connected with the gate spacer.

16. A semiconductor device, comprising:

a substrate having a fin;

a gate structure over the fin;

epitaxial source and drain features over the fin and separated by the gate structure;

an interlayer dielectric layer having first and second portions respectively over the epitaxial source and drain features;

a dielectric feature over the substrate and not overlapping the fin, wherein the dielectric feature has a first portion in the gate structure, a second portion in the first portion of the interlayer dielectric layer, and a third portion in the second portion of the interlayer dielectric layer, wherein the second and third portions of the dielectric feature are both in direct contact with the first portion of the dielectric feature; and

first and second helmet portions respectively partially wrapping around the second and third portions of the dielectric feature, wherein the first and second helmet portions are spaced apart from each other, the gate structure is interposed between the first and second helmet portions, and top surfaces of the first and second helmet portions are substantially co-planar with a top surface of the gate structure.

17. The semiconductor device of claim 16 ,

wherein the first and second helmet portions separate the epitaxial source and drain features from the dielectric feature, respectively.

18. The semiconductor device of claim 16 ,

wherein the first portion of the interlayer dielectric layer is further between the first helmet portion and the fin.

19. The semiconductor device of claim 16 , wherein a bottom surface of the first portion of the dielectric feature is lower than a bottom surface of the second portion of the dielectric feature.

20. The semiconductor device of claim 16 , wherein the dielectric feature is a single piece of continuous material.