Sapphire has the characteristics of high hardness, high brittleness, and chemical stability, which are the strengths as an optical material, but also the difficult points in processing. In order to obtain a sapphire wafer with an ultra-smooth finished surface, the following processing methods can be used:
The principle of hydration polishing: during the ceramic polishing machine processing, there is the friction between the polishing disk and the sapphire surface, of which the contact point generates high temperature and high pressure. Because of the activated atoms on the sapphire surface, a hydrous chemical reaction layer is formed on its surface when the hot water vapor molecules interact with water on it. Then with the help of hot water vapor, it takes advantage of the friction between the polishing disk and the sapphire surface to remove the hydration layer on the sapphire surface, so as to achieve an ultra-precision processing surface. It is a polishing method that utilizes the workpiece to generate a hydrous chemical reaction at the interface. The entire processing process of sapphire wafer avoids the surface scratches on the workpiece without using abrasives and polishing liquids, which is relatively green and environmentally-riendly.
The principle of laser polishing: it can be divided into two methods through the thermal and photochemical action of laser and sapphire: cooling polishing and heat polishing. Cooling polishing removes the material by adopting a short-wavelength laser to decompose material chemically. After the sapphire surface material absorbs light molecules, the structure of its surface will be destroyed, so that the surface material can leave the body to realize the material removal. Heat polishing generally uses continuous long-wavelength lasers to remove the surface components of the material by melting, evaporation, etc. However, it is likely to cause cracks and rough surface on account of the great thermal temperature gradient and the thermal stress, which is more suitable for rough polishing. While the cooling polishing is more suitable for ultra-precision polishing for that the thermal stress is small in the polishing process, so cracks are rarely generated.
Those above are only two of the most suitable processing methods for sapphire wafers. It is an inevitable trend that the grinding industry will develop towards energy conservation and environmental protection in the future.