Atomic level surface roughness of epoxy resin induced by novel chemical mechanical polishing with high material removal rate and its mechanisms elucidated using molecular dynamics simulations and density functional theory

Abstract

Epoxy resins are widely used in the coating, adhesive and electronics industries. However, it is a difficult-to-machine polymer owing to its nature of thermal softening and soft-plastic and corrosion resistance characteristics. To overcome these difficulties, surface roughness (S_a) is usually set at more than 4 nm, and material removal rate (MRR) is normally set lower than 2 μm h⁻¹ during traditional chemical mechanical polishing (CMP). Nevertheless, atomic level surface roughness is desired by high-performance devices of epoxy resins. This poses a challenge in conventional CMP. To address this challenge, herein, a novel CMP was developed, and the CMP slurry included ceria, dichloromethane, sodium carboxymethyl cellulose and deionized water. After CMP, an atomic level surface roughness was achieved with an S_a of 0.198 nm, and the MRR was 5.46 μm h⁻¹. To the best of our knowledge, both the surface roughness and MRR are the best values reported in the literature. An atom-molecular dual-scale model was proposed to investigate the dynamically interactive mechanism between dichloromethane and the epoxy resin. Fourier transform infrared and Raman spectroscopies revealed that the conformation of epoxy resin varied and surface swelling occurred during the diffusion of dichloromethane. Hydrogen atoms of dichloromethane were selectively adsorbed onto the oxygen atoms of ether bonds in the epoxy resin, reducing the energy of the chains. The adsorption energy was high, reaching up to −67.3 kcal mol⁻¹, and this conformation was the most stable. During adsorption, 0.012 eV of energy was transferred to dichloromethane from the small crosslinked molecules. Molecular dynamics simulations and density functional theory were used to perform these calculations. Dichloromethane relaxed the resin surface, speeding up the migration rate of chains and reducing their energy of breaking. The combined effect of mechanical shear force, compressive force and relaxation of swelling led to the breakage of C–N bonds with the lowest energy in the chains. The broken short chains were wrapped in dichloromethane, separating from the surface of the resin with the slurry flow. Our results provide new insights into acquiring an atomic level epoxy resin surface with soft-plastic, thermal softening and corrosion resistance characteristics.