Role of Additive Structure on Controlling Ceria/Substrate Interactions Relevant to Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP)

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Chemical Mechanical Polishing (CMP) has emerged as a critical process step for achieving global planarization in advanced integrated circuit manufacturing and has lead to the extension of Moore’s Law. Specifically, Shallow Trench Isolation (STI) CMP is used in the electrical isolation of the active components in an integrated circuit by actively removing TEOS and stopping on Si3N4 to achieve angstrom level uniformity and limit defectivity. Planarization of the overburden material is achieved through a balance of an applied mechanical force and the delivery of a colloidal dispersion (slurry) containing ceria (CeO2) nanoparticles, complexing additives, and rheology modifiers to the substrate surface. Currently, STI slurries contain chemical additives that selectively boost material removal rate (MRR) as well as enhance selectivity via non-covalent passivation films formed at the polishing substrate surface. A crucial factor in maintaining a high MRR is the presence of CeO2 surface oxygen vacancies, commonly associated with Ce3+surface oxidation state, which can be achieved either from pre-dispersion particle processing or though additive/nanoparticle surface reactions present in the slurry formulation. This study probed the impact of the slurry additive functionality, such as carboxylic acids, amines, and phenols, on the removal rate and post-CMP defectivity. Results suggest that the Ce3+ oxidation state is critical to performance but the Ce4+ oxidation state is also a viable reaction site as long as it remains uncomplexed and free of any site-blocking additives. The additive adsorption to the CeO2 surface will result in altering the dynamic interplay of the abrasive particle/chemistry at the substrate surface shifting CMP performance. Employing and correlating a suite of modified analytical methods, such as atomic force microscopy (AFM), electrochemical quartz crystal nanobalance (EQCN), dynamic contact angle measurements, fluorescence microscopy, pre/post characterization of particle properties (size and zeta potential), and dynamic contact angle, a strong correlation between surface energy and CMP performance metrics has been uncovered.