Sapphire is uniquely suitable for sensor windows of electro-optical systems due to its high transparency, high mechanical strength, and chemical inactivity. Unfortunately, these same characteristics also cause polishing of sapphire windows to be extremely difficult and slow. Hence the challenge is to develop a process for affordable production of large area sapphire windows with low-roughness, low-stress and without surface and subsurface damage. Here we report a novel rapid chemical mechanical polishing process that increases the material removal rate during polishing of sapphire by greater than twofold over conventional processes. Such a process can also produce angstrom level surface finish.
A new reactive chemical mechanical polishing process has been developed and optimized for polishing CVD SiC mirror samples. The studies show that the abrasives, chemical nature of the slurry, and other additives play an important role in the material removal rate and surface finish of the SiC mirror. The use of different abrasive types and sizes resulted in differing roughness and removal rates. The smaller abrasives created surface defectivity or higher roughness. This can be explained by different polishing rates of different orientations of SiC grains, resulting in the grain enhancement. Under optimal conditions with appropriate abrasive particles, roughness RMS as low as 0.2 nm was achieved on CVD SiC samples. The process also did not show any scratch-like features in the optical interferometry measurements.