Plasma cleaning of semiconductor and metal surfaces is a long-standing, widespread practice in many areas, including microelectronics fabrication [1], [2] and [3]. While O2-based plasma cleaning is often used to remove C surface contamination, this poses obvious problems in the cleaning of very thin metal films, including interconnect lines. Therefore, cleaning by, e.g., H2, noble gas or NH3 plasmas is of interest. In many interconnect or packaging processing procedures, even a few monolayers of surface contamination may significantly impact subsequent metallization or other processes [4]. In order to address this issue, Co and Cu surfaces were subjected to controlled plasma exposure, and then transferred under rigorously controlled ultra-high vacuum (UHV) conditions to a UHV analysis chamber for XPS characterization of surface composition.