A distinctive material removal mode in chemical mechanical polishing besides chemical bonding and mechanical plowing: Shear slipping

Abstract

Layered materials, such as bismuth, offer exceptional properties for future integrated circuits (IC). Research is underway to adapt these materials to conventional IC manufacturing processes, like chemical mechanical polishing (CMP). However, CMP of layered materials remains underexplored. This study chose bismuth as a representative to investigate its CMP properties. The results reveal that the material removal rate (MRR) increases rapidly and stabilizes as the H₂O₂ concentration increases. An ultra-high MRR exceeding 10 μm/min is achieved, which is significantly higher than the typical <1 μm/min. A distinctive material removal mode is proposed: shear slipping. This mode differs from the previously reported chemical bonding and mechanical plowing. Specifically, bismuth is oxidized by H₂O₂ to form a Bi₂O₃ surface film, which has a weak interaction with the bismuth substrate, creating a low-shear interface. Under the shearing action of the polishing pad asperities, the surface film slips relative to the substrate, distinct from forming and tearing chemical bonds via chemical bonding and breaking the weakened surface in-plane via mechanical plowing. Consequently, material removal is achieved as micron-sized debris. Furthermore, the shear slipping mode may apply to other layered materials. Adding lubricants and optimizing the polishing pad may help control layered materials removal in CMP.