Silicon oxynitride prepared by chemical vapor deposition as optical waveguide materials

This work explores the technology for preparing low hydrogen-content silicon oxynitride film for integrated optical waveguide applications. Plasma-enhanced chemical vapor deposition with N₂O, NH₃ and SiH₄ precursors was used for the oxynitride preparation. The flow rates of the precursor gases are varied to study processing effects on the refractive index and the content of hydrogen bonds. The refractive index of the oxynitride film can be readily tuned between 1.47 and 1.92 by varying the gas flow rates. The composition and the bonding structure of the oxynitride films were investigated with Fourier transform infrared (FTIR) spectroscopy. Results showed that the silicon oxynitride deposited with gas flow rates of NH ₄/N₂O/SiH₄=10/400/10 (sccm) has favorable properties for integrated waveguide applications. The refractive index of this layer is about 1.5 and the layer has a comparative low density of N-H bonds. The high content of O-H bond can be readily eliminated with high-temperature annealing of the as-deposited film in nitrogen ambient. Annealing at temperature of 1000 °C or above which can significantly suppress both the N-H bonds and O-H bonds is preferred. Waveguide devices built with oxynitride prepared at those conditions would have properties of low propagation loss and small size.