Semiconductor devices and methods of fabricating the same

A semiconductor device, comprising:

• a substrate;
• a semiconductor fin protruding from the substrate;
• a P-type device over the semiconductor fin, including:
• a first gate structure engaging with a first channel region of the semiconductor fin;
• a first source/drain (S/D) feature adjacent the first gate structure;
• a dipole layer over the first S/D feature and including a first metal and a second metal different from the first metal;
• and
• a first silicide layer over the dipole layer, the first silicide layer including the first metal;
• and
• an N-type device over the semiconductor fin, including:
• a second gate structure engaging with a second channel region of the semiconductor fin;
• a second S/D feature adjacent the second gate structure;
• and
• a second silicide layer directly contacting the second S/D feature, the second silicide layer including the first metal and having a composition different from that of the dipole layer.

A method, comprising:

• forming a semiconductor layer protruding from a substrate, wherein the semiconductor layer includes a first channel region and a second channel region;
• forming a first source/drain (S/D) feature in the semiconductor layer adjacent the first channel region and a second S/D feature adjacent the second channel region, wherein the first S/D feature includes silicon germanium doped with a P-type dopant and the second S/D feature includes silicon doped with an N-type dopant;
• depositing a metal halide over the first S/D feature and the second S/D feature to form a first metal layer and a second metal layer, respectively, wherein the metal halide includes a first metal;
• and
• subsequently depositing a metal precursor having a second metal over the first S/D feature and the second S/D feature, thereby forming an interfacial layer to directly contact the first S/D feature, a first silicide layer over the interfacial layer, and a second silicide layer to directly contact the second S/D feature, wherein the first silicide layer and the second silicide layer each include the second metal that is different from the first metal, and wherein the interfacial layer differs from the second silicide layer in composition.