It has been observed that CMP removal rate of copper varies for films from different sources. While the film hardness and static wet etch rate in the absence of inhibitors are similar for various films, the static etch rate in the presence of inhibitors is significantly different. Analysis by AFM, XPS, and ion beam sputtering showed the film roughness and surface composition were different for different Cu films within 160 angstroms of the surface. Thus the different in Cu CMP removal rates can be explained by a synergetic effect of copper film roughness (grain size), surface composition, and effective adsorption of inhibitors. This explanation suggests that if polishing is initiated by an aggressive polishing step, removal rate of the remaining bulk copper films become more consistent. Based on these findings, the polishing slurry and process were further optimized.