A method includes providing a structure that includes a semiconductor substrate, an epitaxial source/drain feature over the semiconductor substrate, and one or more dielectric layers over the epitaxial source/drain feature; etching a hole into the one or more dielectric layer to expose a portion of the epitaxial source/drain feature; forming a silicide layer over the portion of the epitaxial source/drain feature; forming a conductive barrier layer over the silicide layer; and applying a plasma cleaning process to at least the conductive barrier layer, wherein the plasma cleaning process uses a gas mixture including N2 gas and H2 gas and is performed at a temperature that is at least 300° C.