Spectroscopic Ellipsometry and Photoluminescence Measurements of as-Deposited and Annealed Silicon Rich Oxynitride Films

As-deposited and annealed amorphous SiO_xN_y/H (0.17 ≤ x ≤ 0.96; 0.07 ≤ y ≤ 0.27) films were characterized by spectroscopic ellipsometry and room temperature photoluminescence measurements. The refractive index of as-deposited silicon oxynitride films could be successfully varied between SiO₂ and a-Si with increased silicon content. As-deposited films were annealed under inert conditions at 400-800 °C for 4 h. Annealing conditions were insufficient to nucleate silicon nanocrystals in the films. High temperature annealing facilitated the hydrogen diffusion out of the film. This led to the reduced thickness and increased refractive index of the silicon rich oxynitride film. A correlation was seen between the changes in the refractive index, optical band gap, E₀₄ (energy corresponding to an absorption coefficient of 10⁴ cm^{- 1}) and Urbach Energy as a function of composition and annealing conditions. The influence of annealing conditions on the photoluminescence spectra of silicon rich oxynitride films has been investigated. The room temperature luminescence in annealed SiO_0.96N_0.27:H films was attributed to the formation of oxygen related defects in these films. In other films, the bonded hydrogen as well as silicon and nitrogen content, played an extremely important role in determining the influence of annealing conditions on the photoluminescence spectra.