Sapphire, whether used as a substrate in the field of optoelectronics or a window in the field of optical communications, has very high requirements for its processing quality. For example, when used to grow GaN by means of metal organic chemical vapor deposition (MOCVD), sapphire substrates is required to have ultra-smooth and non-damaged surface. Currently, the ultra-smooth surface refers to a surface with a surface roughness of less than 1 nm (RMS) and the non-damaged surface means that the processed surface must have a complete surface lattice without processed deterioration layer.
Due to the high hardness of sapphire (Mohs 9.5, only second to diamond of Mohs 10.0) and high brittleness, its mechanical processing is very difficult, and the non-damage super-smooth surface preparation technology is more complicated. Therefore, the industrial preparation of high-quality sapphire crystal element technology that meets the needs of optoelectronics and optical communications is a very complex engineering system, which involves crystal structure, ultra-precision processing, physical chemistry, mechanical manufacturing and other related interdisciplinary subjects. But because of the important application of sapphire components in aerospace, military, etc., sapphire wafer processing technology is extremely confidential in Western countries.
Nowadays, most sapphire wafer manufacturers still adopt the traditional production technology of optical glass, thus are unable to process ultra-smooth, high-quality sapphire wafers with no damage layer to meet the need of optoelectronics and microelectronics. Now they have developed such technics for large-size sapphire wafers, as plastic grinding mechanism, nano-level grinding technology, non-damaged float chemical mechanical polishing. Using atomic force microscope (AFM) as the main inspection tool, through the analysis of the plastic domain grinding and chemical mechanical polishing process of sapphire wafers, manufacturers are able to stably produce super smooth sapphire wafer without damaged layer.
