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

Abstract

Silicon Oxynitride (SiON) layers are grown from SiH 4/N 2, NH 3 and N 2O by Plasma Enhanced Chemical Vapor Deposition (PECVD). The process is optimized with respect to deposition of layers with excellent uniformity in the layer thickness (δ d<1%), high homogeneity of the refractive index (Δ n=2–7×10 −4) 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 dB/cm 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.