Silicon Dioxide, a kind of low index material, is used more widely than any other crystalline compound. Many excellent properties of SiO2 film have been noted, such as its transparency in visible and ultraviolet light, good property of adherence to most of oxides film, high deposition rate, high hardness of film and excellent environmental stability, and so on, SiO2 can be used in multi-layer coatings for laser mirrors, anti-reflection coatings, filters, beam splitters, and thin-film capacitors.