(237p) Rheology of Silica Nanoparticle Dispersions Under High Shear

The role of Chemical Mechanical Polishing (CMP) in semiconductor industry has become more pronounced as companies create smaller and smaller integrated circuit devices. CMP relies on the capability of producing colloidally-stable dispersions for abrasion and to transport the waste products away from the polished surface. Unstable dispersions at high polishing shear rates (~ 1,000,000 s^-1) increase the possibility of forming particle clusters leading to surface scratching. In addition, the impact of particles shape and size on rheological behavior of slurries can determine the smoothness of the final polished surface. In the present study, the shear thickening and stability of commercially available colloidal silica slurries of two different particle sizes was tested using high shear rheology. Rheological measurements were conducted using a specialized experimental protocol uses a parallel plate geometry at 30 to 50 micron gaps, which allows for shear rates ranging from 100-200,000 s^-1. The results collected from these processes are compared to fumed silica slurries under the same conditions. The effect of additives on slurry behavior for particle systems using salts showed the possibility of altering the thickening shear rate to lower/higher values. In addition, for spherical silica slurries with particle sizes ranging from 10 to 110 nm, an analysis of the effect of volume fraction on slurry behavior was conducted by observing the differences between the experimental data and predictions using hard sphere volume fraction-viscosity models.