Preparation of silicon nitride films at room temperature using double-tubed coaxial line-type microwave plasma chemical vapor deposition system

Silicon nitride films were prepared at room temperature using the double-tubed coaxial line-type microwave plasma chemical vapor deposition system. The dependence of film composition and properties on the flow rate of SiH₄ gas and on the partial pressure of N₂ gas in the deposition chamber has been investigated. A new simple method was suggested and employed to determine the film composition from the refractive index and nitrogen concentration. The flow rate of SiH₄ gas was varied between 1 and 10 ml/min. The flow rate of N₂ gas was at 50 ml/min and the partial pressures of N₂ gas in the deposition chamber were set at 0.015 and 0.0036 Torr by changing the size of the substrate table. With an increasing flow rate of SiH₄ gas, the following effects upon the films were obtained: proportional increases in the deposition rate, shifts to lower energy of the absorption edge, decreases in the film density, and decreases in the concentration of N and the N-H bond. Increases in the refractive index, the Si/N ratio, and the concentrations of Si and the Si-H bond were also observed. In the case of low partial pressure of N₂ gas, the deposition rate decreases, the absorption edge shifts to higher energy, the N concentration increases, and the films become denser. The optical properties of the film vary slowly with the flow rate of SiH₄, and these properties can be determined more precisely by varying the flow rate of SiH ₄.