Plasma enhanced chemical vapor deposition silicon oxynitride optimized for application in integrated optics

Silicon Oxynitride layers are grown from SiH4/N2, NH3 and N2O by Plasma Enhanced Chemical Vapor Deposition. The process is optimized with respect to deposition of layers with excellent uniformity in the layer thickness, high homogeneity of the refractive index and good reproducibility of the layer parameters. The optical losses of slab-type waveguides is determined to be as low as 0.2 dB/cm at 632.8 nm wavelength. Due to absorption of N–H and Si–H vibrational overtones, the optical losses in the third telecommunication window, around 1550 nm, is increased to about 2 dBrcm for low index layers. By an anneal step, however, the hydrogen content of the films can be reduced as is confirmed by IR-spectroscopy and the optical losses decrease to below 0.2 dB/cm. Based on the optimized PECVD SiON technology, a layer structure fulfilling the strong requirements of telecommunication devices, is designed for operation at 1550 nm wavelength. This structure, consisting of a SiON core layer (n=1.4857) surrounded by thick oxide cladding layers (n=1.4637), has the potential for realization of channel waveguides allowing for low-loss bends with a small bending radius and high fiber-to-chip coupling efficiency.