Achieving ultralow surface roughness and high material removal rate in fused silica via a novel acid SiO2 slurry and its chemical-mechanical polishing mechanism

Fused silica is widely used as a substrate material in various optical precision devices, and its surface quality plays a significant role in determining the optical performance. However, it is difficult to achieve an ultra-smooth surface without obvious damage using traditional planarization techniques. In this work, we report on the simultaneous achievement of ultralow surface roughness of ~0.193 nm and high material removal rate of ~10.9 μm h−1 on a fused silica substrate via a novel acid SiO2 slurry. The results show an improvement of removal rate by ~900% compared to its alkaline counterpart. Comprehensive studies based on thermogravimetric analysis, infrared X-ray photoelectron spectroscopy, and nuclear magnetic resonance spectra reveal that phenolic hydroxyl in the acid SiO2 slurry plays a critical role in achieving high material removal rate during the chemical-mechanical polishing process, by well-distributing the SiO2 abrasives with an average size of only ~80 nm. This approach delivers the high surface quality. Evidence in support of this explanation has been obtained using advanced characterization techniques including scanning electron microscopy, atomic force microscopy, and optical interferometry profiling. This novel acid SiO2 slurry is also environmentally friendly with significantly higher durability and stability, which is especially suitable for industrial scale production.