Characterization of SiO2 Slurry Samples Used in Chemical Mechanical Polishing

Large particles and aggregates are detrimental to the performance of chemical-mechanical planarization CMP compounds used for polishing. Size and zeta potential measurements are used to study the interactions between silica particles that lead to the formation of aggregates. 

For DLS measurements, the measured size and the polydispersity of the charged particles depends on the dispersion concentration. In order to measure the real size of the particle, the long range electrostatic interaction between charged particles which influences their diffusion speed should be taken into account. Centrifugation changes the concentration and also the size distribution of a polydispersed system by selectively removing the larger components. This makes both the size and the polydispersity index smaller. The zeta potential was, however, found to be independent of centrifugation time.

The zeta potential of the slurry samples can be measured with the Zetasizer Nano in the disposable capillary cell DTS1070 up to a concentration of around 16% w/v. Centrifugation does not change the chemical environment, like pH and salt content and therefore might be a good approach to measuring the zeta potential of samples at high concentration.  Knowledge of the optimal pH range may benefit both the production and the application of CMP slurries.