| Chemical mechanical polishing (CMP) is a vital step for planarizing multi-level interconnect structures in ultra large-scale integrated circuit applications. The CMP has become the fastest growing semiconductor manufacturing operation in the past decade and is expected to continue its high growth rate with the emergence of next generation interconnect materials such as copper and ultra-low dielectric constant insulators in the coming decade. However, these next generation interconnects, due to their fragility and poor adhesion, are susceptible to CMP-induced defect formation such as microscratches, copper and barrier peeling, low k damage, dishing, and erosion. The state-of-the-art slurries presently designed for polishing copper/silica dielectric use hard aggregate particles (fumed alumina, 100--300 nm in diameter), which, we believe, may not be easily extended to polishing of copper/low k or ultra low k dielectrics.; In this study, we investigate copper CMP using nanoparticle based slurries to reduce the defect formation. The reduction of defect formation, however, is among other considerations such as high removal rate. We examine the nanoscale synergistic chemical and mechanical interactions to determine controlling factors in defectivity and removal rate. Our experimental results indicate that the synergistic effect, that is, the rapid formation of surface passive layer that can be subsequently removed by the nanoparticles without deforming underlying bare copper, is needed to obtain the 'gentle' copper CMP. The removal rate is synergistic, but more dominated by the chemical reaction than by the mechanical abrasion. The formation mechanism of the removable surface layer is investigated. It is suggested that the enhanced the reaction kinetics of the layer formation by addition of chelating agent in the slurry leads to a less dense oxide layer on copper surface that can be removed by the nanoparticles. The role of nanoparticle size and concentration is also studied to understand in what manner the material removal occurs. The results show that the indentation volume of the particle onto the surface layer plays an important role in material removal. |
