PECVD Growth of Thick Silicon Oxynitride for On-Chip Optical Interconnects Applications

Thick oxynitride films were prepared by plasma enhanced chemical vapor deposition (PECVD) with N₂O, NH₃ and SiH₄ precursors. The composition and the bonding structure of the oxynitride films were investigated with Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). 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 comparative low densities of O-H and N-H bonds. The O-H bonds can be readily eliminated with high temperature annealing of the as-deposited film in nitrogen ambient. Annealing at temperature of 1000 degC or above which can significantly suppress both the N-H bonds and O-H bonds is preferred. Simple ridge type waveguide with cross-section of 3 mumtimes2.5 mum for the core layer (n = 1.57) was fabricated. This waveguide is able to transmit signal in either TE or TM mode and the number of mode is eight and the bending radius of the waveguide can be reduced to about 6 mum