Inhibition of Silica Nanoparticle Adhesion to Poly(vinyl alcohol) Surfaces by Ammonia-Mediated Hydration: Implications for Effective Post-Chemical-Mechanical Planarization Cleaning

Adhesion of silica abrasive nanoparticles to a poly(vinyl alcohol) (PVA) brush surface in post-CMP (chemical-mechanical planarization) cleaning leads to serious problems in yield enhancement of semiconductor fabrication. However, the nanoscale adhesion mechanism and its correlation with process conditions have hardly been understood. In this study, we investigated the influence of ammonia in the cleaning solution on silica nanoparticle adhesion to a PVA surface. By atomic force microscopy (AFM), we directly measured adhesion forces between a nanoscale silica probe and a PVA brush surface in various solutions and found that ammonia has a significant inhibitory effect against silica nanoparticle adhesion to a PVA surface. Importantly, we found that this effect cannot be explained by the electrostatic interactions alone but also involves steric repulsion between silica and hydrated PVA. We also performed molecular-scale three-dimensional scanning force microscopy (3D-SFM) imaging and contact angle measurements and found that ammonia promotes hydration and swelling of PVA. Furthermore, we performed molecular dynamics simulations and found that ammonia promotes dynamic rearrangements of hydrogen-bonding networks (HBNs) at a PVA-water interface, giving extra flexibility to the PVA chains. Such flexibility promotes local swelling of PVA and inhibits silica nanoparticle adhesion to a PVA surface. This provides important guidelines for optimizing nanoscale structures and interactions of brush surfaces and abrasive nanoparticles in post-CMP cleaning.