Surfactant Effect on Oxide-to-Nitride Removal Selectivity of Nano-abrasive Ceria Slurry for Chemical Mechanical Polishing

Abstract

Through a chemical mechanical polishing (CMP) test using oxide and nitride blanket film wafers, we investigated the effect of adding an anionic surfactant to a ceria slurry, especially at very dilute concentrations (less than 0.2 wt%). The removal rate trend, which decreases with increasing surfactant concentration, was compared with the variation in the electrokinetic behavior of the ceria abrasives dispersed in the slurry. The removal rate transition did not coincide with the changes in the zeta potential or the secondary particle size distribution of the abrasives. This suggests that the electrostatic effect is not the dominant factor in the removal rate with ceria slurry. It is also found that abrasive size influences removal rate trend versus surfactant concentration, and that oxide removal follows Preston's law but nitride removal shows non-Prestonian behavior. To explain the result qualitatively, we have proposed a hydrodynamic model in which a particle travels through the viscous fluid and approaches the film surface.