Epitaxial Structures for Fin-Like Field Effect Transistors

A semiconductor structure, comprising:

• a first fin and a second fin protruding from a semiconductor substrate;
• isolation features disposed over the semiconductor substrate to separate the first and the second fins, wherein a top surface of each of the first and the second fins is below a top surface of the isolation features;
• inner fin spacers disposed along inner sidewalls of the first and the second fins;
• outer fin spacers formed along outer sidewalls of the first and the second fins, wherein the outer fin spacers have a height less than that of the inner fin spacers;
• a source/drain (S/D) structure disposed over the first and the second fins, wherein a top portion of the S/D structure that laterally spans from the first fin to the second fin is substantially parallel to top surfaces of the first fin and the second fin;
• and
• an air gap disposed in the S/D structure, wherein the air gap includes a top portion disposed over the inner fin spacers.

A semiconductor structure, comprising:

• a first fin and a second fin protruding from a semiconductor substrate;
• isolation features disposed over the semiconductor substrate to separate the first and the second fins, wherein a top surface of each of the first and the second fins is below a top surface of the isolation features;
• inner fin spacers disposed along inner sidewalls of the first and the second fins;
• outer fin spacers formed along outer sidewalls of the first and the second fins, wherein the outer fin spacers have a height less than that of the inner fin spacers;
• an air gap disposed between and protruding over the inner fin spacers;
• and
• a source/drain (S/D) structure disposed over the first and the second fins, wherein the S/D structure includes an epitaxial layer disposed over the inner fin spacers, wherein the epitaxial layer and top surfaces of the inner fin spacers define a top portion of the air gap, and wherein a top portion of the S/D structure that laterally spans from the first fin to the second fin is substantially parallel to top surfaces of the first fin and the second fin.