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.