Role of Molecular Structure on Controlling the Dynamic Equilibrium of the Ecosystem Present in Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP) Slurry Formulations

Abstract

Chemical Mechanical Planarization (CMP) has emerged as a critical process step for achieving angstrom-level uniformity in advanced integrated circuit manufacturing and has ultimately lead to the extension of Moore’s Law. This work specifically looks at Shallow Trench Isolation (STI) CMP, which is used in the electrical isolation of the active components in an integrated circuit by actively removing oxide overburden and stopping on Si3N4 to achieve global planarity and limit defectivity. This planarity is achieved through the synergistic balance of an applied mechanical force and the incorporation of a colloidal dispersion (slurry) containing ceria (CeO2) nanoparticles, rheology modifiers, and stability additives. In addition to the aforementioned additives, a main initiative of STI slurry formulation development has been centered around oxide rate control and selectivity enhancement. Current research has emphasized the addition of compounds that contain carboxylic acid, amine, and amino acid functionality. While the mechanism behind these additives is still of great debate, results have shown the importance of additive surface adsorption and nanoparticle surface redox properties. More specifically, in order to achieve optimal performance, the slurry additive must not impede the presence of surface oxygen vacancies on the nanoparticle, which are known to facilitate high oxide material removal rate (MRR). Slurry additives with redox activity as well as antioxidant properties show the highest MRR due to an increase in the surface oxygen vacancies and a decrease in the non-productive surface interactions. A suite of dynamic, analytical techniques such as atomic force microscopy (AFM), contact angle measurements, pre/post characterization of particle properties (size and zeta potential), coefficient of friction (COF), and UV-Vis spectroscopy, were employed. Results indicate a strong correlation between additive structure, slurry macro-environment, and overall CMP performance.