Semiconductor device and manufacturing method thereof

A method of forming a semiconductor device, comprising:

• forming an epitaxial source/drain (S/D) structure to be in lateral contact with semiconductor channel layers, wherein the semiconductor channel layers are vertically separated from one another;
• forming a gate structure around the semiconductor channel layers;
• covering the epitaxial S/D structure and the gate structure with a dielectric structure;
• forming a trench in the dielectric structure to accessibly expose at least a portion of the epitaxial S/D structure;
• forming a metal layer in the trench;
• annealing the metal layer to form a contact feature from the portion of the epitaxial S/D structure within the trench and metal residues remaining on a sidewall of a spacer of the dielectric structure in the trench, wherein after the annealing and before etching the metal residues, the metal residues expose portions of the spacer of the dielectric structure in the trench;
• etching the metal residues by an etchant solution having an oxidation potential at least 1.4V;
• and
• forming a S/D contact in the trench to be in contact with the contact feature overlying the epitaxial S/D structure.

A method of forming a semiconductor device, comprising:

• forming an epitaxial source/drain (S/D) structure to be in lateral contact with semiconductor channel layers along a first direction, wherein the semiconductor channel layers are separated from one another in a second direction that is substantially perpendicular to the first direction;
• forming a gate structure around the semiconductor channel layers;
• forming a trench in a dielectric structure that covers the epitaxial S/D structure and the gate structure to accessibly expose at least a portion of the epitaxial S/D structure;
• forming a contact spacer on the dielectric structure and in the trench, wherein the contact spacer lands on a periphery of a top surface of the portion of the epitaxial S/D structure;
• forming a metal layer in the trench;
• reacting the metal layer with the epitaxial S/D structure to form a silicide feature, wherein after the reacting and before a wet etching process, metal residues remain on a sidewall of the contact spacer in the trench to expose portions of the contact spacer in the trench;
• selectively removing the metal residues without damaging the contact spacer through the wet etching process;
• and
• forming a metal contact in the trench to be in contact with the contact spacer and the silicide feature overlying the epitaxial S/D structure.