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.
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