Interfacial Layer Between Fin and Source/Drain Region

A method of manufacturing a semiconductor device, the method comprising:

• forming a first fin and a second fin with an isolation region interposed between the first fin and the second fin;
• forming a dummy gate structure over the first fin and the second fin;
• forming a first recess in the first fin and a second recess in the second fin proximate the dummy gate structure;
• forming a first interfacial layer in the first recess and a second interfacial layer in the second recess, the first interfacial layer being a discrete layer from the second interfacial layer;
• and
• growing an epitaxial source/drain region over the first interfacial layer and the second interfacial layer, wherein the first interfacial layer and the second interfacial layer has an atomic percent content of germanium lower than the first fin, the second fin, and the epitaxial source/drain region.

A semiconductor structure comprising:

• a substrate;
• a first fin and a second fin on the substrate, wherein the first fin and the second fin comprise silicon germanium having a first silicon atomic percent content;
• a first interfacial layer over the first fin, wherein the first interfacial layer comprises silicon germanium having a second silicon atomic percent content, wherein a surface roughness of the first interfacial layer is less than a surface roughness of the first fin underlying the first interfacial layer;
• a second interfacial layer over the second fin, wherein the second interfacial layer comprises silicon germanium having the second silicon atomic percent content, wherein a surface roughness of the second interfacial layer is less than a surface roughness of the second fin underlying the second interfacial layer;
• and
• a source/drain region on the first interfacial layer and the second interfacial layer, wherein the source/drain region comprises silicon germanium having a third silicon atomic percent content, wherein the second silicon atomic percent content is greater than the third silicon atomic percent content and the first silicon atomic percent content.