Silicon Nitride Film and Emission Spectrum in a Silane-Nitrogen Plasma

Abstract

The depostition of silicon nitride film at room temperature using a low frequency (50 Hz)silane (SiH₄)-nitrogen (N₂) mixture plasma CVD was investigated. The refractive index (n) and the resistivity of the film was 2.0 and about 10¹⁵ ohm cm respectively, These v alues were comparable with those of Si₃N₄ grown by thermal CVD process. Silicon nitride films with n =2.0 were obtained at SiH₄ (10%)-N₂ (90%) mixtures at a total pressure of 1.2 Torr with about 1.5 W input power, and the growth rate of the film was 80Å/min. Moreover, it was found that both n and the film thickness ( t) were approximately proportional to the amount of N₂ (k%) in the mixture. The emission spectrum of the low frequency plasma in the SiH₄ -N₂ mixtures was measured with a monochromator in a wavelength range from 2000Å to 8000Å. The emission of emitting excited states of Si, SiH, H, H₂ and N₂ in the SiH₄-N₂ mixture plasma could only be confirmed. The plot of the Si emission intensity against k had a maximum. Moreover, the emission intensity of the 2 nd positive band from N₂ excited molecules increased exponentially with increasing k. These results were discussed from the standpoint of the collision of the excited N₂ molecule and Si atom. No difinite relationship between the Si emission intensity and the properties of the film could be found.