An electron-spin resonance study of the structure of plasma-deposited silicon-oxynitride films

Abstract

We have measured electron-spin resonance spectra of silicon-oxynitride layers grown by plasma-enhanced chemical vapor deposition from gas mixtures of SiH4, N2O, and NH3. The analyses were performed on untreated, thermally annealed, and gamma irradiated samples. A relatively small spin density (about 1017 cm−3) is found for the as-deposited layers. Since the resonances remain weak upon annealing, gamma irradiation was performed in order to acquire more structural information on the silicon-oxynitride network. The evolution of the spin density upon annealing is discussed in relation to the hydrogen release during annealing. In the as-deposited and annealed samples, g values were found close to 2.0055. This strongly suggests the presence of silicon clusters in the material. Spin densities remain low upon annealing unless we anneal at temperatures as high as 1000 °C. For these temperatures, smaller g values are observed. Irradiation with gamma rays induces similar signals except for oxygen-rich samples. These show a narrow line at a g value of about 2.001, which can be ascribed to E′ centers. The intensity of this signal falls rapidly with decreasing oxygen content, which implies that these materials are not made up of a mixture of a silicon-nitride and a silicon-oxide phase.