Channel formation in gate-all-around complementary metal-oxide-semiconductor devices

A method, comprising:

• forming a sacrificial gate structure over channel regions of first and second fins;
• removing the sacrificial gate structure to expose the channel regions of the first and second fins;
• removing sacrificial layers from the first and second fins to form a plurality of first suspended layers in the first fin and a plurality of second suspended layers in the second fin, wherein the first and second suspended layers include a same first semiconductor material;
• forming a mask covering the first suspended layers;
• while the first suspended layers are covered by the mask, performing a doping process to introduce a second semiconductor material that differs from the first semiconductor material into the second suspended layers;
• removing the mask;
• after the removing of the mask, performing an anneal process to adjust a distribution of the second semiconductor material in the second suspended layers;
• and
• forming a metal gate stack wrapping around each of the first and second suspended layers.

A semiconductor structure, comprising:

• a substrate;
• a first nanostructure suspended above the substrate and extending lengthwise along a first direction;
• a second nanostructure suspended above the substrate and extending lengthwise along the first direction;
• a gate stack engaging the first nanostructure to form an n-type transistor and engaging the second nanostructure to form a p-type transistor, wherein in a top view of the semiconductor structure the gate stack extends lengthwise along a second direction perpendicular to the first direction;
• and
• gate spacers disposed on sidewalls of the gate stack,
• wherein in a first cross-sectional plane cut along the second direction and perpendicular to a top surface of the substrate, the gate stack wraps around the first and second nanostructures, and the second nanostructure is thicker than the first nanostructure and includes a material composition different from the first nanostructure.