Silicon nitride thin-films deposited by radiofrequency reactive sputtering: Refractive index optimization with substrate cooling in a nitrogen-rich atmosphere

Silicon nitride (SiN) is widely used as a core material in optical waveguides due to its optical properties. The deposition of SiN thin-films by radiofrequency (RF) reactive sputtering is commonly used in low-temperature processes, where the thin-films optical properties can be optimized by controlling the deposition parameters (sputtering power, gases ratio, etc.). This work presents the deposition of several SiN thin-films by RF reactive sputtering with different sputtering powers (ranging from 180 W to 300 W), with a nitrogen-argon ratio of 16:4, and performing substrate cooling in a nitrogen-rich atmosphere immediately after deposition, consisting in keeping the substrate under 16 sccm of nitrogen until it reaches 25 °C. The refractive indices of the SiN thin-films were assessed through ellipsometry, obtaining a maximum refractive index of 1.906 at 400 nm. SiN thin-films were also analyzed by energy-dispersive spectroscopy (EDS) and atomic force microscopy (AFM).