Atomic-scale study on nanoparticle removal mechanism during post-Cu CMP cleaning process using ReaxFF MD

Abstract

The removal of silica (SiO₂) nanoparticles on the surface of the copper (Cu) wafer during the post chemical mechanical polishing process has not yet been researched at the atomic level, making it difficult to achieve nanoparticle-free cleaning performance. In this work, the deposition and removal processes of SiO₂ nanoparticles on Cu (1 1 1) surface in water, ammonium hydroxide and citric acid were studied by reactive force field molecular dynamics (ReaxFF-MD) simulation. The surface state of the copper substrate after pretreatment, the chemical bond evolution, and the mechanisms of different chemicals on nanoparticle removal were researched. The results show that water molecules promote the cleavage of Si-O-Cu bonds through chemical decomposition. Ammonium hydroxide dehydrogenates water molecules adsorbed on the copper surfaces to form hydroxyl groups through dissociation reaction, thereby increasing the electrostatic repulsion and suppressing the deposition. Simultaneously, more surface damage is produced since it could enhance the reactivity of Cu atoms. Citric acid could chemically adsorb onto the Cu substrate, hindering the contact between nanoparticles and the copper surface and promoting the lateral movement of nanoparticles. This work provides atomistic insights into the wafer cleaning process after chemical mechanical polishing, which is of great significance for the design of cleaning solutions.