Role of polymer additives in an aqueous cerium oxide slurry for the chemical and mechanical polishing of wafers with shallow trench isolation

Objectives. The work set out to investigate the optimal presence of functional additives in an aqueous cerium oxide slurry to ensure the colloidal stability of abrasive particles and predict slurry behavior during the chemical and mechanical polishing of wafers with shallow trench isolation. Methods. The pH of the slurry was measured using a Crison GLP 22 pH meter ( Crison Instruments, S.A., Spain) with a Crison 5201 electrode. Elemental analysis was performed by inductively coupled plasma mass spectrometry (ICP-MS) using a Spectro MS spectrometer ( Shimadzu , Japan). Infrared (IR) spectra were recorded in absorption–reflection mode using a Simex FT-801 Mikran-3 micro-Fourier transform IR spectrometer ( SIMEX , Russia). The IR spectra were analyzed using the NIST, Hummel, and Aldrich databases. Results. The investigated slurry was confirmed to contain two modifiers. The first was partially ionized (no more than 50%) polyacrylic acid using ammonium (NH 4 + ) as the counterion for the COO − groups, while the second represented a mixture of saturated fatty amides having an alkyl substituent length of at least C 15 . A proposed mechanism for the interaction of the modifiers with the cerium oxide particle involves the adsorption of copolymer segments onto the abrasive via electrostatic interaction through COO − groups and the secondary adsorption of the fatty amide onto the polymer-modified abrasive surface. A block diagram was developed for analyzing the interactions between the modifiers and the abrasive, as well as those involving dielectric surfaces having different chemical natures. Cerium oxide is shown to act as a chemical and mechanical agent that effectively removes only the surface layer of silicon oxide. At the same time, the polyacrylic acid–ammonium polyacrylate copolymer provides electrostatic stabilization of the slurry and topographically dependent passivation of SiO 2 . The fatty amide, comprising a cation-active surfactant in the working pH range of the slurry (4.6), is adsorbed onto the surface layer of silicon oxide to reduce surface energy and facilitate the mechanical work of its layer-by-layer removal. Since the silicon nitride surface remains intact due to its negligeable interaction with water, the adsorption of cation-active surfactant molecules on it is likely due to the passivating effect of the polymeric modifier. Conclusions. The obtained results are important for understanding the active mechanisms of polishing compositions used in the chemical and mechanical planarization for wafers with shallow trench isolation, as well as for optimizing the formulations of new slurries used in microelectronic technologies.