Annealing Behavior Of Silicon Nitride Thin Film Deposited By PECVD

As a kind of multi-functional materials, Silicon nitride thin film is widely used in many fields. In the manufacture of microelectronic materials and devices, silicon nitride thin film is used as passivating film, insulation layer and diffusion mask. In the fabrication of solar cell, silicon nitride thin film is used as passivating film and anti-reflecting film. In the production of luminescent material based on silicon, silicon nitride is used as embed matrix of silicon nanometer clusters. As we all know, annealing is an important process in the above applications of silicon nitride thin films.In the paper, the properties, applications and preparation methods of silicon nitride films were overviewed. Plasma Enhanced Chemical Vapor Deposition (PECVD) was used to prepare silicon nitride thin films in our experiments. Silane and ammonia as gas source, silicon nitride thin films were grown under several conditions of different temperature and different ratio of silane and ammonia. Then the films were annealed in the ambient of nitrogen. Raman, Fourier Transform Infrared spectrum (FTIR), X-ray Photoelecton Spectrum (XPS) and X-ray Diffraction Spectrum (XRD) were used to analyze the nature and annealed properties of silicon nitride films. Annealing effects on the structure and properties of films were discussed and the results of the experiments could be useful referrence when designing the process parameters of silicon nitride thin films in manufacture.Firstly, silicon nitride thin films were grown on several substrates at the temperature of 100³50℃, with the flow ratio of SiH₄ and NH₃ 1:3 and the power 20W. Rich silicon films were obtained, the ratio of Si and N is about 1.5:1, and the structure unit is Si₃N₂. Rich bonded H was found in the films in the form of Si-H and N-H. As the temperature rised, the content of H in the films decreased, and the density of the films increased.In the paper, we also found that the structure of silicon nitride thin film annealed at 800℃ changed, and silicon nanometer clusters were found in the film. The higher the deposition temperature is, the more easily the amorphous silicon nanometer clusters formed and crystallized. When the deposition temperature is high enough (e.g. 900℃ or 1000℃), as the annealing time increased, the structure of silicon nitride film changed successively from Si-Si₂N₂ to Si-Si₃N and from Si-Si₃N to Si-Si4. At last silicon clusters formed.At last, silicon nitride film was grown at the temperature of 300°C, with the flow ratio of NH3 and SiH* 1:1, 3:1 and 6:1. The formed films were annealed at 1100°C for 2 hours, and the content of N in the film increased when the flow ratio of NH3 and SiRj increased. As the content of N in the film increased, the number of silicon clusters after annealing decreased.