Method to form a fully strained channel region

A method comprising:

• forming an n-type region on a top portion of a substrate;
• forming a carbon-doped region in a top portion of the n-type region;
• growing a silicon epitaxial layer on the carbon-doped region;
• forming a capping layer on the silicon epitaxial layer;
• forming an opening aligned to the carbon-doped region in the capping layer to expose the silicon epitaxial layer;
• etching the silicon epitaxial layer through the opening to form a recess and expose the carbon-doped region;
• and
• forming an epitaxial stack in the recess, wherein the forming the epitaxial stack comprises:
• forming a seed layer in the recess;
• and
• forming the epitaxial layer on the seed layer to fill the recess.

A structure comprises:

• a fin over a substrate, wherein the fin comprises:
• an n-type doped silicon region;
• a carbon-doped silicon region on the n-doped silicon region;
• a silicon seed layer on the carbon-doped silicon region;
• and
• an epitaxial layer over the silicon seed layer;
• and
• an isolation layer surrounding the n-type doped silicon region of the fin.