Device and method for tuning threshold voltage by implementing different work function metals in different segments of a gate

1. A semiconductor device, comprising:

an active region extending in a first direction; and

a first gate structure extending in a second direction different from the first direction, the first gate structure including a work-function metal layer and a fill-metal layer disposed over the work-function metal layer;

wherein:

the work-function metal layer of the first gate structure includes a first segment that is disposed over the active region and a second segment that is not disposed over the active region;

the first segment has a first material composition;

the second segment has a second material composition different from the first material composition;

both the first material composition and the second material composition include n-type work function metals, or both the first material composition and the second material composition include p-type work function metals; and

the first segment is free from overlapping with the second segment in a top view.

2. The semiconductor device of claim 1 , wherein the active region includes a fin structure.

3. The semiconductor device of claim 2 , wherein the first segment of the first gate structure at least partially wraps around the fin structure.

4. The semiconductor device of claim 1 , wherein: the second segment has a dimension in the top view and is spaced apart from the active region by a distance in the top view, and wherein the dimension is correlated with the distance.

5. The semiconductor device of claim 1 , further comprising a second gate structure extending in the second direction, the second gate structure being spaced apart from the first gate structure in the first direction;

wherein:

the second gate structure includes a third segment that is disposed over the active region and a fourth segment that is not disposed over the active region;

the third segment has a third material composition; and

the fourth segment has a fourth material composition different from the third material composition.

6. The semiconductor device of claim 5 , wherein:

the active region has a boundary that extends in the first direction;

the second segment is spaced apart from the boundary of the active region by a first distance; and

the fourth segment is spaced apart from the boundary of the active region by a second distance that is different from the first distance.

7. The semiconductor device of claim 5 , wherein the second material composition is different from the fourth material composition.

8. The semiconductor device of claim 5 , wherein the first material composition and the third material composition are the same.

9. The semiconductor device of claim 5 , wherein:

the second segment has a first dimension measured in the second direction;

the fourth segment has a second dimension measured in the second direction; and

the first dimension is not equal to the second dimension.

10. The semiconductor device of claim 1 , further comprising: a dielectric isolation structure that at least partially surrounds the active region in the top view, and wherein:

the second segment is disposed over, and in contact with, the dielectric isolation structure; and

the second segment is a continuous extension of the first segment.

11. A semiconductor device, comprising:

an active region spanning along a first direction;

a first elongated gate spanning along a second direction substantially perpendicular to the first direction, wherein the first elongated gate includes a first portion that is disposed over the active region and a second portion that is not disposed over the active region, and wherein the first portion and the second portion include different n-type work function metal materials or different p-type work function metal materials; and

a second elongated gate spanning along the second direction and separated from the first elongated gate in the first direction, wherein the second elongated gate includes a third portion that is disposed over the active region and a fourth portion that is not disposed over the active region, and wherein the third portion and the fourth portion include different n-type work function metal materials or different p-type work function metal materials, and wherein the second portion and the fourth portion have different sizes in the second direction;

wherein the first elongated gate and the second elongated gate are both gate structures of PFETs, or wherein the first elongated gate and the second elongated gate are both gate structures of NFETs;

and wherein:

the active region has a boundary that spans along the first direction;

the second portion is separated from the boundary of the active region by a first distance; and

the fourth portion is separated from the boundary of the active region by a second distance that is greater than or less than the first distance.

12. The semiconductor device of claim 11 , wherein:

the active region includes a fin structure; and

the first portion and the third portion each wrap around the fin structure.

13. The semiconductor device of claim 11 , wherein the second portion and the fourth portion include different materials.

14. The semiconductor device of claim 11 , wherein the first portion and the third portion include same materials.

15. The semiconductor device of claim 11 , wherein:

a size of the second portion in the second direction is correlated with the first distance; and

a size of the fourth portion in the second direction is correlated with the second distance.

16. A method, comprising:

forming a fin structure that extends in a first direction;

forming a dummy gate structure that extends in a second direction different from the first direction;

forming source/drain regions in the fin structure; and

after the forming of the source/drain regions, replacing the dummy gate structure with metal-gate structure having a work-function metal layer and a fill-metal layer, wherein the work-function metal layer includes a first portion formed over the fin structure and a second portion not formed over the fin structure, and wherein the first portion and the second portion include different work-function metals of a same type of conductivity and are both formed after the dummy gate structure has been removed.

17. The method of claim 16 , wherein:

the forming of the dummy gate structure comprises forming a first dummy gate structure and a second dummy gate structure that is spaced apart from the first dummy gate structure in the first direction;

the replacing of the dummy gate structure is performed such that a first metal-gate structure and a second metal-gate structure replace the first dummy gate structure and the second dummy gate structure, respectively;

the first metal-gate structure includes the first portion and the second portion;

the second metal-gate structure includes a third portion formed over the fin structure and a fourth portion not formed over the fin structure; and

the third portion and the fourth portion include different work-function metals.

18. The method of claim 17 , wherein the replacing of the dummy gate structure is performed such that:

the second portion is separated from the fin structure by a first distance measured in the second direction;

the fourth portion is separated from the fin structure by a second distance measured in the second direction; and

the second distance is greater than or less than the first distance.

19. The method of claim 17 , wherein the replacing of the dummy gate structure is performed such that:

the second portion has a first dimension measured in the second direction;

the fourth portion has a second dimension measured in the second direction; and

the second dimension is greater than or less than the first dimension.

20. The semiconductor device of claim 11 , wherein the first elongated gate and the second elongated gate each include a respective work-function metal layer and a respective fill-metal layer disposed over the work-function metal layer, and wherein the first portion, the second portion, the third portion, and the fourth portion are portions of the work-function metal layer.