Method of making a high speed semiconductor device

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, wherein a distance between the gate structure and the first edge structure is different from a distance between the gate structure and the second edge structure;
• 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 a top surface of the buried channel is spaced from a top surface of the semiconductor strip, a bottom surface of the buried channel is closer to the top surface of the semiconductor strip than a bottom surface of the first source/drain feature, and a dopant concentration of the buried channel is highest under the gate structure.

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

• forming a dummy gate structure, a dummy first edge structure and a dummy second edge structure on a semiconductor strip;
• forming a first source/drain feature between the dummy gate structure and the dummy first edge structure;
• forming a second source/drain feature between the dummy gate structure and the dummy 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;
• implanting a buried channel in the semiconductor strip, wherein a top surface of the buried channel is spaced from a top surface of the semiconductor strip, a bottom surface of the buried channel is closer to the top surface of the semiconductor strip than a bottom surface of the first source/drain feature, and a dopant concentration of the buried channel is highest under the dummy gate structure;
• and
• replacing the dummy gate structure with an active gate structure.