Method for forming source/drain contacts

A method, comprising:

• providing a structure that includes:
• a substrate,
• an n-type field effect transistor (NFET) region having a first source/drain (S/D) feature, and
• a p-type field effect transistor (PFET) region having a second S/D feature;
• depositing a dielectric layer over the first and second S/D features;
• etching the dielectric layer to form openings exposing the first and second S/D features;
• forming a masking layer over the first S/D feature in the NFET region while the second S/D feature in the PFET region remains exposed;
• implanting gallium into the second S/D feature while the masking layer is over the first S/D feature to form a gallium-containing implant layer over the second S/D feature;
• removing the masking layer;
• recessing the first and second S/D features with an oxygen-atom-containing etchant, wherein the oxygen-atom-containing etchant converts a top portion of the gallium-containing implant layer into a gallium oxide containing layer;
• removing the gallium oxide containing layer;
• forming a first metal silicide layer over the first S/D feature and a second metal silicide layer over a remaining portion of the gallium-containing implant layer over the second S/D feature;
• and
• forming S/D contacts over the first and second metal silicide layers.

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

• forming a first gate structure and a second gate structure over a substrate;
• forming a first source/drain (S/D) feature adjacent to the first gate structure;
• forming a second S/D feature adjacent to the second gate structure;
• depositing one or more dielectric layers over the first and second S/D features;
• etching the one or more dielectric layers to form openings exposing the first and second S/D features;
• forming a protective layer over sidewalls of the openings and over the first and second S/D features;
• forming a masking layer over the first S/D feature while the second S/D feature remains exposed;
• implanting a metallic dopant into the protective layer over the second S/D feature and into the second S/D feature while the masking layer is over the first S/D feature, thereby forming a metallic-dopant-containing implant layer over the second S/D feature;
• removing the masking layer;
• anisotropically etching the protective layer;
• and
• etching the first and second S/D features with an oxygen-atom-containing etchant, thereby converting a top portion of the metallic-dopant-containing implant layer into a metallic-dopant-oxide-containing layer while a bottom portion of the metallic-dopant-containing implant layer remains on the second S/D feature.