Copper CMP: The Relationship between Polish Rate Uniformity and Lubrication

Chemical Mechanical Polishing of Copper (Cu-CMP) is an important yet poorly-understood nanofabrication technique. In this work, we demonstrate that the degree of non-uniformity in polishing rates, described by the new quantity MRRNU , relates to the lubrication conditions of the polishing couple. MRRNU is the difference between the highest and lowest material removal rates ( MRR s) recorded across the wafer surface, normalized by the average MRR . The polish rate non-uniformity that this quantity encapsulates is shown to transition from negative (wafer-scale dishing) to positive (wafer-scale doming) with increasing Sommerfeld number, for the pad and slurry chemistry used here. This is explained by the presence of co-existing lubrication zones in the pad-wafer interface. Each of the zones described, namely the edge zone , hydrodynamic zone and suppression zone , demonstrate a different relationship between pressure and removal rate, resulting in variation in MRR across the wafer.