Method for forming source/drain contacts

A semiconductor device, comprising:

• a fin protruding from a substrate, the fin having a first source/drain (S/D) region, a second S/D region, and a channel region connecting the first and second S/D regions;
• a gate structure over the channel region of the fin;
• a first S/D feature comprising silicon germanium (SiGe) disposed in the first S/D region of the fin, wherein a top portion of the first S/D feature is doped with gallium (Ga) and a bottom portion of the first S/D feature is free of Ga;
• a second S/D feature disposed in the second S/D region of the fin, wherein the second S/D feature is free of Ga, and wherein in cross-sectional views each along a lengthwise direction of the gate structure, a top surface of the first S/D feature is below a top surface of the second S/D feature;
• a metal silicide layer over the top surface of the first S/D feature;
• and
• an S/D contact disposed on the metal silicide layer and electrically coupled to the first S/D feature.

A semiconductor device comprising:

• an n-type FinFET region including:
• a first gate stack;
• a first gate spacer over sidewalls of the first gate stack;
• an n-type epitaxial feature in a source/drain (S/D) region of the n-type FinFET region;
• and
• a first metal silicide layer over the n-type epitaxial feature;
• and
• a p-type FinFET region including:
• a second gate stack;
• a second gate spacer over sidewalls of the second gate stack;
• a silicon germanium (SiGe) epitaxial feature in an S/D region of the p-type FinFET region, wherein a top portion of the SiGe epitaxial feature includes gallium (Ga);
• and
• a second metal silicide layer over the top portion of the SiGe epitaxial feature,
• wherein a top surface of the n-type epitaxial feature has a first concave profile, a top surface of the SiGe epitaxial feature has a second concave profile, and a lowest point of the first concave profile is below a lowest point of the second concave profile.