Improving the Optical Properties of SiNx:H Thin Film by Optimizing NH3:SiH4 Gas Ratio Using Plasma-Enhanced Chemical Vapor Deposition

Abstract

In this article, we enhance the optical properties of hydrogenated silicon nitride (SiN_x:H) thin film by optimization of deposition conditions using plasma-enhanced chemical vapor deposition (PECVD). Specifically, the impact of varying NH₃:SiH₄ gas ratios (GRs) on the optical and structural properties of the SiNx:H film has been investigated. A ratio of 1.2 results in an optimal refractive index of 2.05, a thickness of 75.60 nm, and a deposition rate of 1.01 nm s⁻¹, achieving the highest optical transmittance of 92.63% at 350 °C. Lower ratios, such as 0.5, produce higher refractive indices up to 2.43 but with reduced transmittance and thinner films (53.67 nm at 84.43% transmittance). The bandgap of GR 1.2 at 350 °C is also calculated as 3.23 eV using Tauc's plot. Fourier transform infrared spectroscopy analysis shows significant variations in SiH hydrogen bonding configurations at different temperatures, affecting SiH and SiNH bond densities. These are crucial for understanding the films’ electronic and optical behaviors, with the highest hydrogen content for SiH noted at 3.30 × 10²² cm⁻³ at 350 °C. This research provides a detailed understanding of how precise control over GRs during PECVD can fine-tune SiN_x film properties, offering guidelines for producing high-quality SiN_x:H layer.