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 has been investigated using excimer laser operating at a wavelength of 193 nm. Single layers of silicon nitride were formed from SiH4/NH3 gas mixture with Si/N atomic ratio of 0.6-0.7. The layers that contained a small amount of hydrogen had a refractive index and extinction coefficient of n = 2, k = 0015 at 600 nm. 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 a amount of Si-H bonds. Decreasing the SiH4/N2O ratio led to the formation of pure silicon dioxide with a refractive index of 1.45. A two layer coating of silicon nitride and silicon dioxide resulted in the formation of an antireflection coating with a reflectivity of about 0.5% at 750 nm. (C) 1998 Elsevier Science S.A. All rights reserved.