Fin field effect transistors including multiple lattice constants and methods of fabricating the same

A Field Effect Transistor (FET) structure, comprising:

• a device isolation layer on a substrate;
• a fin comprising a first lattice constant, the fin extending from the substrate to protrude from the device isolation layer to provide upper side walls of the fin, a top surface of the fin, a channel region, and source/drain interfaces at opposing ends of the channel region;
• a gate structure crossing over the fin opposite the channel region between the source/drain interfaces;
• a first epi layer on the top surface of the fin comprising a second lattice constant different than the first lattice constant;
• a second epi layer, on the upper side walls of the fin and on the first epi layer on the top surface, comprising a third lattice constant different than the first and second lattice constants;
• and
• source/drain regions, comprising a third epi layer including a fourth lattice constant different than the first, second, and third lattice constants, extending from the source/drain interfaces outward from the gate structure to cover the top surface of the fin exposed by the gate structure, wherein the first epi layer is absent from the upper side walls of the fin and the second epi layer is absent from a top surface and side walls of the source/drain regions.

A Field Effect Transistor (FET) structure, comprising:

• a device isolation layer on a substrate;
• a fin comprising a first lattice constant, the fin extending from the substrate to protrude from the device isolation layer to provide upper side walls of the fin and a top surface of the fin and a channel region;
• a gate structure crossing over the fin opposite the channel region;
• a first epi layer on the top surface of the fin comprising a second lattice constant different than the first lattice constant;
• and
• a second epi layer, on the upper side walls of the fin, comprising a third lattice constant different than the first and second lattice constants,
• wherein the first epi layer is absent from the upper side walls of the fin and the second epi layer extends between the upper sidewalls of the fin to cover the first epi layer, and
• wherein the fin includes source/drain interfaces at opposing ends of the channel region, the structure further comprising:
• source/drain regions, comprising a third epi layer including a fourth lattice constant different than the first, second, and third lattice constants, extending from the source/drain interfaces outward from the gate structure to cover the top surface of the fin exposed by the gate structure.

A Field Effect Transistor (FET) structure, comprising:

• a device isolation layer on a substrate;
• an omega shaped silicon structure comprising a first lattice constant, the omega shaped silicon structure extending from the substrate to protrude from the device isolation layer to provide upper side walls of the omega shaped silicon structure and a top surface of the omega shaped silicon structure and a channel region;
• a gate structure crossing over the omega shaped silicon structure opposite the channel region;
• a first epi layer on the top surface of the omega shaped silicon structure comprising a second lattice constant different than the first lattice constant;
• and
• a second epi layer, on the upper side walls of the omega shaped silicon structure, comprising a third lattice constant different than the first and second lattice constants,
• wherein the first epi layer is absent from the upper side walls of the omega shaped silicon structure and the second epi layer extends between the upper sidewalls of the omega shaped silicon structure to cover the first epi layer, and
• wherein the omega shaped silicon structure includes source/drain interfaces at opposing ends of the channel region, the structure further comprising:
• source/drain regions, comprising a third epi layer including a fourth lattice constant different than the first, second, and third lattice constants, extending from the source/drain interfaces outward from the gate structure to cover the top surface of the omega shaped silicon structure exposed by the gate structure.

A Field Effect Transistor (FET) structure, comprising:

• a device isolation layer on a substrate;
• an active semiconductor layer comprising a first lattice constant, the active semiconductor layer extending from the substrate to protrude from the device isolation layer to provide upper side walls of the active semiconductor layer and a top surface of the active semiconductor layer and a channel region;
• a gate structure crossing over the active semiconductor layer opposite the channel region;
• a first epi layer on the top surface of the active semiconductor layer comprising a second lattice constant different than the first lattice constant;
• and
• a second epi layer, on the upper side walls of the active semiconductor layer, comprising a third lattice constant different than the first and second lattice constants,
• wherein the first epi layer is absent from the upper side walls of the active semiconductor layer and the second epi layer extends between the upper sidewalls of the active semiconductor layer to cover the first epi layer, and
• wherein the active semiconductor layer includes source/drain interfaces at opposing ends of the channel region, the structure further comprising:
• source/drain regions, comprising a third epi layer including a fourth lattice constant different than the first, second, and third lattice constants, extending from the source/drain interfaces outward from the gate structure to cover the top surface of the active semiconductor layer exposed by the gate structure.