Multiscale Mechanistic Insights into Green Anionic Surfactants on Chemical Mechanical Polishing Performance of C-, A-, and R-Plane Sapphire: Combined Experiments and Theoretical Calculations

Sapphire slurry should be developed for environmental friendliness, high efficiency, and sustainability. The effects of three green anionic surfactants (dodecyl phosphate, DAP; dodecylbenzenesulfonic acid, DBSA; ammonium dodecyl sulfate, ADS) on C-, A-, and R-plane sapphire chemical mechanical polishing (CMP) were comparatively investigated. The results show that the effects of three surfactants on sapphire slurry and CMP performance are ranked in the following order: DAP < DBSA < ADS. Among them, ADS has the best effect on C-, A-, and R-plane sapphire, with the removal rate of 4.04, 2.11, and 3.20 μm/h and the surface roughness Sq of 0.215, 0.199, and 0.218 nm, respectively. X-ray photoelectron spectroscopy and quantum chemical calculations have jointly confirmed that ADS exhibits the highest reactivity. The adsorption process of surfactants in sapphire CMP was simulated using molecular dynamics (MD), with adsorption energies of -16.5, -4.4, and -4.34 eV for ADS, DBSA, and DAP, respectively, which further indicated that ADS was most likely to react with sapphire. ADS has a dual role in the slurry: it can adsorb on the sapphire surface to improve surface quality, and the NH4+ decomposed from ADS can react with Al(OH)4- to increase the removal rate of sapphire. This work provides a new atomic-scale mechanism for a sapphire CMP.