A type of CMP scratches with an embedded particle and a comet-like tail has been studied. The nature of the embedded particle was found to be silica which suggested that the source came from barrier metal polishing step. The inclusion of a pad-cleaning step during barrier polishing was found to reduce the defect significantly. This pad cleaning step reduce hydrophobicity of the polishing pad. Through a series of experiments, it was found that BTA was the cause of high hydrophobicity build up on during barrier polish and a defect mechanism was proposed. In addition, pad cleaning has positive impact on TDDB. The reason for the the reliability improvement was believed to be due to formation of divots at the side of the trench which, after deposition of a capping nitride layer, will increase resistance for Cu migration during voltage cycle.