Investigation of Deposition Rates in Bilayer Silicon Nitride Structures Using Ellipsometry and the Maxwell Garnett Model

This study investigates the impact of precursor gases on the deposition rate, as well as the geometric and optical properties of silicon oxynitride (SiOxNy) thin films synthesized via low pressure chemical vapor deposition technique using SiH2Cl2, N2O, and NH3 at 850°C. Spectroscopic ellipsometry measurements and the Maxwell Garnett model were employed to analyze the films, treating SiOxNy as a heterogeneous material composed of silicon oxide (SiO2) and silicon nitride (Si3N4). The thickness of SiOxNy films was estimated based on the NH3 gas flow rate, while its refractive index was evaluated at a wavelength of 830 nm with the flow of NH3. Afterwards, the variation in deposition rate was examined as a function of the NH3 flow rate and Si3N4 volume fraction. Results indicate that both film thickness and refractive index increase with higher NH3 flow rates, while the deposition rate rises from 5.745 to 7.979 nm/min as the NH3 flow rises. In contrast, the results show that the volume fraction of Si3N4 increases with the flow of NH3, whereas the SiO2 fraction decreases, reaching a minimum of 72.68% when the flow of NH3 increases. This correlates with the observed reduction in refractive index values ( $${{n}_{{{\text{Si}}{{{\text{O}}}_{x}}{{{\text{N}}}_{y}}}}}$$ ≤ 1.597). Finally, the achieved results suggest that the films obtained are transparent and oxygen-rich layers.