Fabrication of optical waveguide using silicon oxynitride prepared by thermal oxidation of silicon rich silicon nitride

This work reports a method for reducing hydrogen content in silicon oxynitride film for integrated optical applications. The silicon oxynitride (SiON) films were grown by plasma enhanced chemical vapor deposition (PECVD) with N₂O, NH₃ and SiH₄ as precursor gases. Using higher flow rate of SiH₄ and NH₃, Si-rich oxynitride films with high refractive index were obtained. Detailed ellipsometry and Fourier transform infrared (FTIR) spectroscopy characterization of the as-deposited samples and samples with thermal oxidation/annealing were conducted. Results showed that the silicon oxynitride deposited with gas flow rates of NH₃/N₂O/SiH₄=20/500/20 (seem) has favorable properties for integrated waveguide applications. The refractive index of this layer is about 1.57 at 632.8 nm wavelength and the layer has a comparative low density of N-H bonds. With a high temperature annealing treatment in oxygen ambient, the hydrogen content in the as-deposited SiON film was reduced by 87% as results of excess silicon oxidation and hydrogen bond removal. © 2005 IEEE