Application of surface analysis in study on removal mechanism and abrasive selection during fused silica chemical mechanical polishing

In this work, surface analysis technology is employed to investigate the removal mechanism and the selection of abrasive during fused silica chemical mechanical polishing (CMP). Morphology of abrasives is inspected by scanning electron microscope (SEM). The atomic force microscope (AFM) is used to determine the surface roughness (Rq) and undulating (PV) of the polished fused silica surface. The results show that abrasive morphology has a tremendous influence on removal rate (MRR) and PV but has little effect on the Rq. The AFM and infrared spectroscopy (IR) analysis show that a soft layer, called “silica gel membrane (SGM),” existed on the polished surface is the critical reason for the differences of MRR, Rq, and PV during CMP. For three kinds of micro‐ceria abrasives, the abrasive with a rougher surface gets more opportunities to contact the surface of fused silica, yielding higher MRR. Regarding different kinds of nano‐abrasives, there are more SGM induced by nano‐ceria abrasive resulting from higher chemical reaction rate. The element contaminations on the polished fused silica have been assessed using X‐ray photoelectron spectroscopy (XPS), and the results suggest that there are depths of 3.6 and 5.4‐nm element contaminations on the polished surface of fused silica with nano‐ceria and nano‐alumina abrasives, respectively. While the surface polished by nano‐silica is free of heterogeneous element contaminations. Based on study results, a novel polishing slurry is designed by modifying the chemical composition of nano‐silica. Comparing with ceria‐based slurry, the silica‐based slurry has better removal efficiency, and surface quality in fused silica precision machining.