Physical-optical properties of LPCVD amorphous silicon rich-nitride and oxynitride

Low pressure chemical vapour deposition (LPCVD) silicon oxynitride and silicon-rich nitride films of various composition (from pure SiO₂ to pure Si₃N₄) were deposited by changing the relative gas flow ratio N₂O to NH₃ and SiH₂Cl₂ to NH₃, respectively. The effects of oxygen on the physical properties of the films were studied using spectroellipsometry and Fourier transform infrared spectroscopy. The deconvolution of the IR spectra was made. The characteristic absorption peak for Si₃N₄ is at 822 cm^-1 (Si-N bonds), and for SiO_xN_y is around 973 cm^-4 (Si-O-Si bond). Higher oxygen content decreases the refractive index of SiO_xN_y films, whereas more silicon in silicon nitride increases the refractive index. The refractive index dispersion is studied by the single-oscillator Wemple Di Domenico model. The optical gap varies monotonically from 5.43 eV for silicon nitride to 9 eV for HTO LPCVD silicon dioxide, and for silicon oxynitride was found to be around 6 eV