Influence of H on the composition and atomic concentrations of 'N-rich' plasma deposited SiOxNyHz films

The influence of H on the composition and atomic concentrations of Si, O, and N of plasma deposited SiOxNyHz films was investigated. The bonding scheme of H was analyzed by Fourier-transform infrared spectroscopy. The composition and absolute concentrations of all the species present in the SiOxNyHz, including H, was measured by heavy-ion elastic recoil detection analysis (HI-ERDA). Samples were deposited from SiH4, O2, and N2 gas mixtures, with different gas flow ratios in order to obtain compositions ranging from SiNyHz to SiO2. Those samples deposited at higher SiH4 partial pressures show both Si-H and N-H bonds, while those deposited at lower SiH4 partial pressures show N-H bonds only. The Si-H and N-H bond concentrations were found to be proportional to the N concentration. The concentration of H was evaluated from the Si-H and N-H stretching absorption bands and compared to the HI-ERDA results, finding good agreement between both measurements. The deviation from H-free stoichiometric SiOxNy composition due to the presence of N-H bonds results in an effective coordination number of N to produce Si-N bonds lower than 3. By fitting the experimental composition data to a theoretical model taking into account the influence of N-H bonds, the actual concentration of N-H bonds was obtained, making evident the presence of nonbonded H. The presence of Si-H and Si-Si bonds was found to partially compensate the effect of N-H bonds, from the point of view of the relative N and Si contents. Finally, the presence of N-H bonds results in a lower Si atom concentration with respect to the stoichiometric film, due to a replacement of Si atoms by H atoms. This decrease of the Si concentration is lower in those films containing Si-H and Si-Si bonds. A model was developed to calculate the Si, O, and N atom concentrations taking into account the influence of N-H, Si-H, and Si-Si bonds, and was found to be in perfect agreement with the experimental data measured by HI-ERDA