Optimization of SiN thin film for high index contrast planar silica waveguides

Silica based planar lightwave circuits (PLCs) are used in various kinds of wave-guided optical passive devices. In this study, silicon nitride (SiN) thin films were deposited by rf plasma enhanced chemical vapor deposition (PECVD). The SiN thin films were obtained at low temperatures (<350°C) by the decomposition of appropriate gaseous mixtures under suitable rf power and gas flow ratios. The refractive index of the film increased as the SiH ₄/N₂ flow ratio was increased from 0.16 to 1.66. We also studied the chemical composition of the films by X-ray photoelectron spectroscopy (XPS). The thickness, refractive index and surface morphology of the films were characterized by ellipsometry and atomic force microscopy (AFM).