Fabricating high quality, high stress channel regions in gate-all-around field effect transistors (gaa fets)

A method comprising:

• forming a plurality of nanoribbons of crystalline material, wherein forming the nanoribbons comprises:
• forming a first layer on the nanoribbons, the first layer comprising an additive element not in the crystalline material;
• forming a second layer one the first layer;
• and
• heating the nanoribbons, the first layer, and the second layer to diffuse the additive element into the crystalline material;
• and
• after the heating to diffuse the additive element, forming source/drain regions on opposite sides of the nanoribbons.

A method comprising:

• forming a plurality of crystalline nanoribbons;
• forming an additive material layer around each of the nanoribbons, the additive material layer comprising an additive element not in the crystalline nanoribbons;
• forming a capping layer around each of the additive material layers;
• and
• diffusing the additive element into the nanoribbons by heating;
• removing the capping layer;
• forming a first source/drain region on a first side of the nanoribbons comprising the additive material;
• and
• forming a second source/drain region on a second side of the nanoribbons opposite the first side.