Role of interparticle forces during stress-induced agglomeration of CMP slurries

In chemical mechanical polishing (CMP) slurry distribution systems, highly localized shear stresses generated by the pumping devices can cause particle agglomeration, resulting in a significant increase in particle-induced defects. We investigate the role of interparticle forces on stress-induced particle agglomeration in typical silica slurries with various chemicals. Both the maximum interparticle repulsive force and the critical distance at which attractive forces overcome repulsive forces increased with pH for silica slurries. Addition of salt to the slurry led to decrease in both maximum repulsive force and critical distance. These results can be directly correlated to the stability of slurry under shear stress. The degree of agglomeration on particle-induced defectivity was assessed through the CMP of low-k dielectrics.