Reverse selectivity--high silicon nitride and low silicon dioxide removal rates using ceria abrasive-based dispersions.

We show that by adding poly(acrylicacid-co-diallyldimethylammonium chloride), a cationic polymer with a weight average molecular weight of about 4200 g/mole, to ceria-based dispersions, it is possible to achieve a silicon nitride removal rate (RR) of >100 nm/min and a silicon dioxide RR of <2 nm/min at pH 4 and 4 psi down pressure during chemical mechanical polishing. Furthermore, the RRs of the silicon dioxide films can be tuned by varying the polymer to abrasive weight ratio in the dispersion while the nitride RR is unaffected. We also characterized the role of adsorption of this polymer additive on ceria, silica and silicon nitride powders using zeta potential, adsorption isotherms, UV-Vis spectroscopy, contact angle, thermo-gravimetric analysis and friction coefficient measurements. Our results show that the polymer film formed on the ceria particle surface is strongly bound to it, survives use in polishing and appears to control its reactivity with the silicon dioxide surface in conjunction with electrostatic interactions. Copyright 2010 Elsevier Inc. All rights reserved.