Abstract: Silicon nitride (SiN_x) films have been widely used in optoelectronic devices due to their high dielectric constant and good stability, but the thickness of silicon nitride films has an important effect on the performance of devices. In order to solve this problem,silicon nitride films have been grown by plasma enhanced chemical vapor deposition (PECVD) at 13.56 MHz on glass and N-type monocrystalline silicon substrate using high purity NH₃, N₂and SiH₄ as reactant gas sources by optimizing other deposition parameters and changing deposition time. The samples were characterized by X-ray diffraction (XRD), ultraviolet-visible(UV-VIS) light transmittance spectra, fourier transform infrared absorption spectroscopy (FTIR) and scanning electron microscope (SEM). The relationship between deposition time and film thickness and the effect of deposition time on film properties were studied in detail. The results show that the prepared samples are amorphous SiN_x thin film structure and the crystallization is independent of deposition time. The thickness of the thin film increases uniformly with deposition time, the refractive index of the thin film increases with deposition time, and the optical band gap does not change with deposition time. SEM test results show that with the increase of deposition time, the film density and uniformity become better and better. Fourier transform infrared spectra show that the silicon/nitrogen ratio of the thin film does not change with deposition time, but the oxygen content decreases, indicating that the increased film density effectively prevents O atoms from entering the film and prevents the occurrence of oxidation after the thin film is deposited. The experimental results show that good optical properties and dense structure of silicon nitride films can be obtained by changing deposition time.

Key words: plasma enhanced chemical vapor deposition, silicon nitride film, deposition time, optical band gap, refractive index, density