Method of forming semiconductor structure including suspended semiconductor layer and resulting structure

A method of forming a semiconductor structure, the method comprising:

• forming a set of fins over a substrate, wherein each fin in the set of fins includes alternating layers of a sacrificial material and a semiconductor, and includes a lower channel region beneath the alternating layers of the sacrificial material and the semiconductor material, and wherein the set of fins includes a first fin in a first device region and a second fin in a second device region;
• forming a first dopant-containing layer over the set of fins and the substrate;
• exposing the first fin in the first device region by removing the first dopant-containing layer thereover;
• forming a second dopant-containing layer over the exposed first fin in the first device region and over the first dopant-containing layer over the second fin in the second device region;
• exposing an upper portion of each of the first fin and the second fin;
• removing the sacrificial material from each of the first fin and the second fin thereby suspending portions of the semiconductor material over the lower channel region within each of the first fin and the second fin, the suspended semiconductor material being suspended between a pair of spacers on each of the first and second fins;
• performing an anneal to drive dopants from the first dopant-containing layer into the lower channel region of the first fin and to drive dopants from the second dopant-containing layer into the lower channel region of the second fin;
• and
• forming an active gate stack over the lower channel region of each of the first fin and the second fin, the active gate stack substantially surrounding the suspended portions of the semiconductor material of each fin.