Laser induced chemical vapor deposition of optical thin films on curved surfaces

Laser Induced Chemical Vapor Deposition (LCVD) of Silicon nitride and silicon dioxide single and double layers have been investigated using Excimer laser operating at a wavelength of 193 nm The composition of silicon nitride which was formed in SiH4/NH3 gas mixture was nearly stochiometric having a refractive index of 1.8-1.9 and contained small amount of hydrogen. Deposition of silicon dioxide was investigated using SiH4/N2O. Using this gas mixture the film composition depended strongly upon the SiH4/N2O ratio. At high ratio the film formed was silicon oxynitride, which contained both Si-N and Si-O bonds. The film also contained small amount of Si-H bonds. Decreasing SiH4/N2O ratio led to the formation of pure silicon dioxide with a refractive index of 1.45. A double layer coating of both silicon nitride and silicon dioxide resulted in the formation of antireflection coating with a reflectivity of about 0.5% at 750 nm.