Epitaxial Layers in Source/Drain Contacts and Methods of Forming the Same

A method, comprising:

• forming a first trench and a second trench in an interlayer dielectric (ILD) layer to expose a first S/D epitaxial feature formed over a first fin and a second S/D epitaxial feature formed over a second fin, respectively, wherein the first S/D epitaxial feature is of n-type and the second S/D epitaxial feature is of p-type;
• depositing an n-type semiconductor layer in the first trench and the second trench;
• forming a germanium-containing (Ge-containing) layer over the n-type semiconductor layer;
• removing the Ge-containing layer from the first trench, wherein the removing removes the n-type semiconductor layer from the second trench;
• forming a silicide layer over the n-type semiconductor layer in the first trench and over the second S/D epitaxial feature in the second trench;
• and
• forming a S/D contact over the silicide layer in the first trench and the second trench, respectively.

A semiconductor structure, comprising:

• a first source/drain (S/D) epitaxial feature of a first conductivity type disposed in a semiconductor layer, the first S/D epitaxial feature having a first resistivity;
• a second S/D epitaxial feature of a second conductivity type different from the first conductivity type disposed in the semiconductor layer, wherein the first S/D and the second S/D epitaxial features are disposed adjacent their respective metal gate structures;
• at least one epitaxial semiconductor material layer disposed over the first S/D epitaxial feature, wherein the at least one epitaxial semiconductor material layer has a second resistivity, the second resistivity being lower than the first resistivity;
• and
• a first S/D contact and a second S/D contact disposed over the at least one epitaxial semiconductor material layer and over the second S/D epitaxial feature, respectively, wherein a bottom surface of second S/D contact is below a bottom surface of the first S/D contact.