Study of Agglomeration Behavior of Chemical Mechanical Polishing Slurry under Controlled Shear Environments

Abstract

The presence of large oversize particles (>0.5 μm) in the slurry is known to cause polishing defects during chemical mechanical planarization/polishing (CMP) process. One of the reasons for presence of large particles in the slurry is due to usage of pumps during slurry delivery. The shear rate of pumps is known to cause agglomeration problem in CMP slurries, with increasing shear rate leading to increase in agglomeration in the slurries. However, till now all the work on shear-induced agglomeration has been qualitative or at best semi-quantitative in nature. In the present work, a novel technique to study agglomeration behavior as a function of quantified shear rates has been developed. A rheometer was used as a means to subject slurry to different shear rates for various times. The resulting change in oversize particle distribution was measured using a single particle optical sensing (SPOS) system. It was observed that the behavior of silica slurry when subjected to different shear rates falls into three regions namely de-agglomeration, transition region and agglomeration region. This technique provides a deterministic way for slurry stability and can be used as a guide for design of slurry, slurry selection and design of slurry delivery systems.