Atomic force microscopy study of the role of molecular weight of poly(acrylic acid) in chemical mechanical planarization for shallow trench isolation

The influence of the molecular weight of poly(acrylic acid) (PAA) on chemical mechanical planarization (CMP) for shallow trench isolation (STI) was investigated. The adsorption behaviors of PAA as a function of molecular weight on deposited plasma-enhanced tetraethylorthosilicate and chemical vapor deposition Si₃N₄ films were analyzed by the force measurement using atomic force microscopy (AFM). The AFM results revealed that the affinity of PAA with the nitride film is higher than the affinity with the oxide film, and thus a denser adsorption layer on the nitride film is formed with higher molecular weight of PAA, which leads to higher selectivity in STI CMP. Additionally, to determine the correlation between the dispersion stability of the CeO₂ resulting from the presence of PAA with different molecular weight and CMP performance, the colloidal properties of the slurry as a function of the molecular weight of PAA were examined.