Method of making a semiconductor device

1. A method of fabricating a semiconductor device, the method comprising:

forming a gate structure, a first edge structure and a second edge structure on a semiconductor strip;

forming a first source/drain feature between the gate structure and the first edge structure;

forming a second source/drain feature between the gate structure and the second edge structure, wherein a distance between the gate structure and the first source/drain feature is different from a distance between the gate structure and the second source/drain feature; and

implanting a buried channel in the semiconductor strip, wherein the buried channel is entirely below a top-most surface of the semiconductor strip, a maximum depth of the buried channel is less than a maximum depth of the first source/drain feature, and a dopant concentration of the buried channel is highest under the gate structure.

2. The method of claim 1 , wherein implanting the buried channel comprises implanting dopants to define a top surface of the buried channel a distance of about 2 nanometers (nm) to about 7 nm below the top-most surface of the semiconductor strip.

3. The method of claim 1 , wherein implanting the buried channel comprises implanting the buried channel across less than an entire width of the semiconductor strip.

4. The method of claim 1 , further comprising:

forming a first contact over the first source/drain feature; and

forming a second contact over the second source/drain feature, wherein a top-most surface of the first contact is coplanar with a top-most surface of the second contact.

5. The method of claim 4 , further comprising forming a gate contact over the gate structure, wherein a top-most surface of the gate contact is coplanar with the top-most surface of the first contact.

6. The method of claim 1 , wherein forming the first edge structure comprises forming the first edge structure partially over an isolation feature.

7. The method of claim 1 , wherein forming the first source/drain feature comprises forming the first source/drain feature extending above the top-most surface of the semiconductor strip.

8. The method of claim 1 , wherein forming the second source/drain feature comprises forming the second source/drain feature about 1.5 to about 4.5 times farther from the gate structure than the first source/drain feature is from the gate structure.

9. A method of fabricating a semiconductor device, the method comprising:

forming a gate structure, a first edge structure and a second edge structure on a semiconductor strip;

forming a first source/drain feature between the gate structure and a first edge of the semiconductor strip;

forming a second source/drain feature between the gate structure and a second edge of the semiconductor strip, wherein a distance between the gate structure and the first source/drain feature is different from a distance between the gate structure and the second source/drain feature; and

implanting a buried channel in the semiconductor strip, wherein the buried channel is entirely below a top-most surface of the semiconductor strip, a maximum depth of the buried channel is less than a maximum depth of the first source/drain feature, and an entirety of the buried channel is between the first source/drain feature and the second source/drain feature.

10. The method of claim 9 , wherein at least one of forming the first source/drain feature or forming the second source/drain feature comprises using an epitaxial process.

11. The method of claim 9 , wherein forming the first source/drain feature comprises forming the first source/drain feature extending above a top surface of the semiconductor strip.

12. The method of claim 9 , further comprising forming an isolation feature adjacent to the semiconductor strip.

13. The method of claim 12 , wherein forming the first edge structure comprises forming the first edge structure overlapping the isolation feature.

14. The method of claim 9 , wherein forming the first source/drain feature comprises forming the first source/drain feature a first distance from the first edge structure.

15. The method of claim 14 , wherein forming the second source/drain feature comprises forming the second source/drain feature the first distance from the second edge structure.

16. A method of fabricating a semiconductor device, the method comprising:

forming a gate structure on a semiconductor strip;

forming a first source/drain feature between the gate structure and the first edge structure;

forming a second source/drain feature between the gate structure and the second edge structure, wherein a distance between the gate structure and the first source/drain feature is different from a distance between the gate structure and the second source/drain feature; and

implanting a buried channel in the semiconductor strip, wherein the buried channel is entirely below a top-most surface of the semiconductor strip, a maximum depth of the buried channel is less than a maximum depth of the first source/drain feature, and a dopant concentration of the buried channel is highest under the gate structure.

17. The method of claim 16 , wherein implanting the buried channel comprises implanting the buried channel offset from a periphery of the semiconductor strip by a first distance.

18. The method of claim 17 , wherein the first distance ranges from about 2 nanometers (nm) to about 7 nm.

19. The method of claim 17 , wherein implanting the buried channel comprises implanting the buried channel the first distance below the top-most surface of the semiconductor strip.

20. The method of claim 16 , wherein forming the second source/drain feature comprises forming the second source/drain feature to define a ratio between the distance between the gate structure and the first source/drain region to the distance between the gate structure and the second source drain region ranging from about 1.5 to about 4.5.