Effect of slurry aging on stability and performance of chemical mechanical planarization process

Chemical mechanical planarization (CMP) is known to be one of the most challenging processes in microelectronics manufacturing due to the number of variables involved in the design of the process. In particular, the slurries made of nano-sized particles and aggressive chemistries need to be characterized batch to batch and as a function of time to enable robust high volume manufacturing. In this study, the effect of slurry aging on CMP performance was investigated systematically for regular silica based slurry as well as for slurry containing an organic biocide additive to prevent bacteria formation. The parameters examined were particle size distribution, zeta potential, bacteria count, total organic carbon concentration, silicon ion dissolution, material removal rate (MRR), and surface quality. The results indicated that aging influenced slurry performance negatively and even with the addition of biocide, organic contamination was observed at the extended aging periods. The material removal rates decreased significantly by aging and more surface deformations were observed on the wafer surfaces polished with the slurries destabilized with the elapsed time. Slurries containing biocide were detected to be more prone to agglomeration and increase in particle size as the time passes after the slurry is exposed to the environment. Furthermore, the impact of short time slurry aging (conditioning) on particle properties of the slurries containing polymeric additives and the adverse affects of extreme stability in the slurries containing surfactants are also discussed in terms of the two other factors that can cause variability in CMP slurry performance.