Structure and method for transistor with line end extension

1. A semiconductor structure, comprising:

an isolation feature formed in a semiconductor substrate;

a first fin and a third fin, adjacent to the first fin, extending in a first direction on the semiconductor substrate and a second fin and a fourth fin, adjacent to the second fin, extending in the first direction on the semiconductor substrate and being collinear with the first fin and third fin respectively, wherein the isolation feature interposes the first fin and the second fin, and the isolation feature interposes the first fin and the third fin, such that a first contiguous region of insulating material is disposed between the first fin and the third fin, and a second contiguous region of insulating material is disposed between the first fin and the second fin;

a first active region in the first fin and a second active region in the second fin, wherein the first and second active regions extend in a first direction and are separated from each other by the second contiguous region of insulating material of the isolation feature;

a dummy gate disposed on the second contiguous region of insulating material of the isolation feature and extending over end regions of at least the first fin and the third fin;

a first functional gate disposed on the first active region and configured to form a first field effect transistor;

a second functional gate disposed on the second active region and configured to form a second field effect transistor;

a first epitaxy source/drain feature formed in a trench in the first active region of the first fin and interposing the first functional gate and the dummy gate in the first direction, wherein a bottom edge of the first epitaxy feature is below a top surface of the isolation feature and wherein a sidewall of the trench nearest the dummy gate is defined by a semiconductor material of the first fin,

wherein the first epitaxy source/drain feature is separated from the second contiguous region of insulating material of the isolation feature by a portion of the semiconductor material of the first fin the portion having a length in the first direction that is defined by a distance the dummy gate extends over the end region of the first fin.

2. The semiconductor structure of claim 1 , wherein

the semiconductor substrate includes silicon;

the first epitaxy source/drain feature includes silicon germanium; and

the first field transistor includes one of a p-type field effect transistor and a n-type field effect transistor.

3. The semiconductor structure of claim 1 , further comprising a second epitaxy feature formed on the second active region and interposing the dummy gate and the second functional gate.

4. The semiconductor structure of claim 3 , wherein

the second epitaxy feature includes silicon carbide; and

the second field transistor includes one of a p-type field effect transistor and a n-type field effect transistor,

wherein the second epitaxy feature is separated from the second contiguous region of insulating material of the isolation feature another portion of the semiconductor substrate.

5. The semiconductor structure of claim 1 , wherein the first and second functional gates each include a high k dielectric material layer and a metal layer on the high k dielectric material layer.

6. The semiconductor structure of claim 1 , wherein the isolation feature is a shallow trench isolation (STI) feature and the second contiguous region of insulating material of the isolation feature extends a first dimension S1 in the first direction.

7. The semiconductor structure of claim 6 , wherein

the dummy gate aligned in a second direction perpendicular to the first direction and spanning a second dimension S2 in the first direction,

wherein the second dimension is greater than the first dimension.

8. The semiconductor structure of claim 7 , wherein

the dummy gate extends to the first active region with a first overlap dimension Z1 in the first direction; and

the dummy gate extends to the second active region with a second overlap dimension Z2 in the first direction, wherein the S1, S2, Z1 and Z2 are related in a formula S2=S1+Z1+Z2.

9. The semiconductor structure of claim 8 , wherein

the dummy gate includes a main gate stack and a gate spacer disposed on both sides of the main gate stack;

the main gate stack has a width W in the first direction and the gate spacer has a thickness T; and

the second dimension S2 is equal to W+2T.

10. The semiconductor structure of claim 1 , further comprising:

a third active region in the third fin;

a third functional gate disposed on the third active region and configured to form a third field effect transistor; and

a third epitaxy feature formed in the third active region and interposing the third functional gate and the dummy gate, wherein the third epitaxy feature is separated from the second contiguous region of insulating material by a second portion of the semiconductor substrate having a second length, wherein the second length is defined by a distance the dummy gate extends over the end region of the third fin.

11. A semiconductor structure, comprising:

first plurality of adjacent fin-like active regions formed in a silicon substrate and oriented in a first direction;

second plurality of adjacent fin-like active regions formed in the silicon substrate and oriented in the first direction;

a shallow trench isolation (STI) feature formed in the silicon substrate and interposed between the first plurality of adjacent fin-like active regions and the second plurality of adjacent fin-like active regions;

a dummy gate disposed on the STI feature and oriented in a second direction substantially perpendicular to the first direction, wherein the dummy gate has a length that extends in the first direction to extends over end regions of the first plurality of adjacent fin-like active regions from one side and extending over end regions of the second plurality of adjacent fin-like active regions from another side;

a first functional gate oriented in the second direction and disposed on each of the first plurality of adjacent fin-like active regions;

a second functional gate oriented in the second direction and disposed on each of the second plurality adjacent of fin-like active regions; and

a first source/drain epitaxy feature formed on a first fin of the first plurality of adjacent fin-like active regions, wherein a bottom and two opposing sidewalls of the first source/drain epitaxy feature interface the first fin of the silicon substrate, wherein the first source/drain epitaxy feature interposes the first functional gate and the STI feature and is substantially coplanar with the STI feature, wherein the first source/drain epitaxy feature is separated from the STI feature by a portion of the first fin of the silicon substrate having a length of silicon material in the first direction, the length defined by a distance the dummy gate extends over the end region of the first fin.

12. The semiconductor structure of claim 11 , wherein the first plurality of fin-like active regions each include a first end contacting the STI feature and the second plurality of fin-like active regions each include a second end contacting the STI feature.

13. The semiconductor structure of claim 12 , wherein

the STI feature spans a first dimension S1 in a first direction;

the first ends and the second ends have a first distance in the first direction, wherein the first distance is equal to the first dimension S1; and

the dummy gate spans a second dimension S2 in the first direction, S2 being greater than S1.

14. The semiconductor structure of claim 13 , wherein

the dummy gate overlaps with the first fin-like active regions of a first overlap dimension Z1 in the first direction;

the dummy gate overlaps with the second fin-like active regions of a second overlap dimension Z2 in the first direction; and

S1, S2, Z1 and Z2 are related in a formula S2=S1+Z1+Z2.

15. The semiconductor structure of claim 11 , wherein the STI feature includes a top surface lower than top surfaces of the first and second fin-like active regions.