Study of Ceria Settling in CMP Slurry

Colloidal stability is a basic requirement for CMP slurry to have stable performance. Due to its high density and high gravity pulling force, ceria particles in CMP slurries cannot be suspended homogenously in static state for long period of time. Improperly mixing can result in changing in CMP performance due to inhomogeneous distribution of ceria particles at different layers of slurry tank. In this work, we collect experimental data how different size of ceria particles and concentration affects the settlement and compare the ceria particles settlement data to the formulated ceria slurry. The ceria particles with larger size will settle faster than smaller size but particle concentration and additives in STI slurry has little impact on particle settlement dynamics. In the formulated ceria, the settlement of ceria particles can change the balance of abrasive to silicon oxide inhibitor ratio and has adversary effect on oxide polishing rates.