Method for forming source/drain contacts

A semiconductor device, comprising:

• 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;
• a first S/D feature comprising silicon germanium disposed in the first S/D region, wherein a top portion of the first S/D feature is doped with gallium and a bottom portion of the first S/D feature is free of gallium;
• a second S/D feature disposed in the second S/D region, wherein the second S/D feature is free of gallium;
• a metal silicide layer over a 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 transistor 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 transistor region;
• and
• a first metal silicide layer over the n-type epitaxial feature;
• and
• a p-type transistor region including:
• a second gate stack;
• a second gate spacer over sidewalls of the second gate stack;
• a silicon germanium containing epitaxial feature in an S/D region of the p-type transistor region, wherein a top portion of the silicon germanium containing epitaxial feature also contains gallium, wherein a bottom portion of the silicon germanium containing epitaxial feature is free of gallium, and wherein a thickness of the bottom portion of the silicon germanium containing epitaxial feature is greater than a thickness of the top portion of the silicon germanium containing epitaxial feature;
• and
• a second metal silicide layer over the top portion of the silicon germanium containing epitaxial feature.