Investigation of optical and chemical bond properties of hydrogenated amorphous silicon nitride for optoelectronics applications

The aim of this work is to determine optimal deposition parameters of silicon nitride for optical applications. The authors present the investigation of hydrogenated amorphous silicon nitride SiN x :H deposited by the low temperature PECVD method in high frequency reactors. The study of hydrogen bonds in the SiN x :H thin films were detailed. The impact of NH 3, SiH 4 and N 2 flow ratio and radio frequency power on optical coefficients in relation to chemical composition and roughness of the film is studied. The correlation between chemical bonds (N–H, Si–H) and refractive index and extinction coefficients is systematically verified. The experimental results show that the films with high refractive indexes superior to 2.05 and low roughness of about 0.35 nm can be achieved for optoelectronics applications by tuning the flow ratio or decreasing the RF power. A variety of processes have been suggested as compatible with low thermal budget (under 350 °C) in order to integrate optical waveguides with lower loss. In particular, the incorporation of N 2 as dilution gas is suited to the fabrication of SiN x :H films optical waveguide requiring low N–H bonds, low concentration of hydrogen [H] and high refractive index.