The influences of post Cu chemical-mechanical-polish cleaning time on time dependent dielectric breakdown (TDDB) and electro-migration (EM) are reported. Cu residue remaining on the porous-low-k (pLK) film surface between Cu lines is a significant factor in TDDB lifetime when the cleaning time is short. In contrast, a longer cleaning time generates low Cu residue on the pLK surface but results in high Cu surface roughness, which leads to TDDB degradation. For EM performance, slightly higher roughness could improve the adhesion of the dielectric barrier layer to the Cu surface, thus increasing its mean time to failure. Further increases in Cu surface roughness, caused by extended cleaning, may generate a seam in the dielectric barrier layer at the deep-recessed trench area. The seam degrades the adhesion strength of the dielectric barrier to Cu and is the initiating site of Cu migration. As a result, it significantly degrades the EM lifetime. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.033111jes] All rights reserved.