Study on Ceria–Silica Interaction in Various Ce3+ Concentration for Effective Post Chemical Mechanical Planarization (CMP) Cleaning
Authors: Myong Kyong Kyu , Byun Jinuk , Choo Min-ju , Kim Hojoong , Kim Jun Yong , Lim Taeho , Kim Jae Jeong 
Published: December 2020

Shallow trench isolation (STI) is a technology that isolates transistors by constructing trenches and filling them with silicon dioxide. The excess silica should be removed by a subsequent step, chemical mechanical planarization (CMP) process, without any damage to active area. To prevent the damage during polishing, the silicon nitride is used for a stopping layer.1 Therefore, in the CMP process in STI, oxide-to-nitride polishing selectivity is needed. Since ceria nanoparticles (NPs) has high removal rate on silicon oxide but low removal rate on silicon nitride, they are generally utilized for CMP in STI.2 Additionally, Ce3+ concentration on the ceria NPs is considerably related to the oxide-to-nitride selectivity. It was reported that as the Ce3+ concentration on ceria NPs increased, its oxide-to-nitride selectivity was improved.3

However, after CMP process, there exists large amount of contaminants on the substrates which is mainly originated from the abrasives and organic additives in CMP slurry. Especially, on the surface of silicon oxide, the residual ceria NPs caused problems in post-CMP cleaning. Since they have chemical interaction with silicon oxide as reported, they are not easily removed from the surface. As the demands for high-end semiconductor devices with enhanced performance soar, the contaminants should be successfully removed.4-6 Therefore, in-depth research on ceria-silica interaction for effective post-CMP cleaning receives large attention.
We directly investigated the ceria-silica interaction using atomic force microscope (AFM) and quartz crystal microbalance (QCM). Using AFM, the adhesion energy between silicon oxide and ceria NPs was quantitatively measured with respect to Ce3+ concentration on the ceria NPs as shown in Figure 1. We changed the surface Ce3+ concentration on the ceria NPs using hydrogen peroxide and ultrasonication, which was classified as Ceria1 to Ceria4.7 Moreover, the adsorption behavior of ceria NPs on the surface of silicon oxide was observed by QCM depending on the surface Ce3+ concentration. From the results of adsorption rate, the activation energy for the ceria-silica adsorption was studied depending on the Ce3+ concentration on the ceria NPs, which is exhibited in Figure 2.
Figure Captions
Figure 1. Adhesion energy between ceria and silica depending on surface Ce3+ concentration.
Figure 2. Plot of the natural logarithm of adsorption rate versus the reciprocal of temperature at different surface Ce3+ concentrations of ceria NPs.
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Figure 1