Silicon-Oxynitride Layers for Optical Waveguide Applications

We report on the fabrication and characterization of silicon-oxynitride (SiON) layers for applications as planar optical
waveguides in the 1550-nm wavelength region. The optically guiding SiON waveguide core layer has a relatively high refractive index of 1.500 and is sandwiched between two silicon-oxide cladding layers with a lower refractive index of 1.450. The SiON layer is deposited by PECVD using silane, nitrous-oxide, and ammonia as gaseous precursors. Waveguide bends with a radius of curvature as small as 1.5 mm can be realized because of the high refractive index
difference achievable between core and cladding layers. This allows the fabrication of compact, relatively complex integrated optical waveguide devices. The deposition process and the characterization of the SiON films are discussed. The strengths of this high refractive index contrast planar waveguide technology is illustrated using the example of an optical add/drop filter for wavelength division multiplexing applications in the field of optical communication systems.