Date of Award
Doctor of Philosophy
Chemical mechanical planarization (CMP) is a mainstream semiconductor processing method for achieving local and global wafer planarization. However, the CMP process fundamentals are poorly understood, and thereby inhibit migratability of lab-scale experiments to production processes. This work addresses the synergistic role of chemical dissolution rate (CDR) and mechanical abrasion rate (MAR) on the material removal mechanisms during CMP process.;A set of nano-wear experiments on elecro-plated copper surfaces are conducted with systematic exposure to active slurry. Initial results of in situ wear test in chemically active slurry showed an increased material removal rate (MRR) relative to a dry wear test. A phenomenological MRR model based on scratch-intersections was formulated to understand the role of consumables and the process parameters. To further understand the synergistic effects between CDR and MAR, two plausible mechanisms of material removal are investigated. Mechanism-I is based on chemical dissolution enhancing MAR. A soft layer of chemical products is assumed to be formed on top of the polished surface due to chemical reaction with a rate much faster than the MAR. It is then followed by a gentle mechanical abrasion of that soft layer. It is found that, for pure copper exposed to ammonium hydroxide, the yield strength of film is about 50% of the substrate yield strength; the modulus of film is about 20% of the substrate modulus. The film thickness is found to be in the order of few nanometers, and increases with the exposure time according to first order linear kinetics. Mechanism-II is based on mechanical abrasion accelerating CDR. In this case, the nano-wear experiment is first performed to generate local variation of the residual stress levels, and then followed by chemical exposure to investigate the variation of the wear depth and the evolution of surface topography. It is found that the residual stress caused by the mechanical wear enhances the CDR, as manifested by the increase of wear depth.;The developed understanding from these experiments can be used in future studies to control the relative rates of CDR and MAR as well as investigating the various process-induced defects.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Che, Wei, "Synergy between chemical dissolution and mechanical abrasion during chemical mechanical polishing of copper " (2005). Retrospective Theses and Dissertations. 1229.