Atomic insights into material removal mechanism in chemical mechanical polishing of silicon using a developed abrasive-free slurry

The atomic surface of silicon (Si) wafers without particulate contamination achieved by chemical mechanical polishing (CMP) is highly desired for advanced chip manufacturing. Traditional CMP processes usually employ abrasive-containing slurries, resulting in significant particulate residues and high-cost post-treatments. To address this challenge, a novel abrasive-free CMP slurry including only a designated chain-length alkylamine was developed based on the observed dependence between the Si surface roughness and alkylamine chain length. After polishing with the long-chain hexylamine slurry, an atomic surface without particulate contamination is achieved with a surface roughness as low as 0.13 nm, which is 85% lower than that obtained using the short-chain methylamine slurry, while maintaining a material removal rate of 57.7 nm/min. Furthermore, we established an atomic mechanistic framework that integrates interfacial chemistry with mechanical action to understand how alkylamine chain length modulates mechanochemistry in abrasive-free Si CMP. Density functional theory calculations show that long-chain alkylamines adsorb more readily but have a milder weakening effect on Si–Si bonds, whereas short-chain counterparts, despite weaker adsorption, more effectively weaken these bonds. Nanowear tests and X-ray photoelectron spectroscopy corroborate that the dynamic equilibrium between the adsorption strength and bond weakening promotes the formation of a mechanically vulnerable reaction layer composed of O_x–Si–N_y compounds, which is amenable to abrasive-free removal for atomic smoothness. Our findings shift the mechanistic paradigm from conventional abrasive-containing interfacial interactions to abrasive-free, chemically driven, adsorption-controlled removal processes. These insights offer theoretical guidelines for both academic research and industrial practice in ultra-precision manufacturing and advanced semiconductor processing.