Influence of H on the composition and atomic concentrations of 'N-rich' plasma deposited SiO_(x)N_(y)H_(z) films

摘要

The influence of H on the composition and atomic concentrations of Si, O, and N of plasma deposited SiO_(x)N_(y)H_(z) 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 SiO_(x)N_(y)H_(z), including H, was measured by heavy-ion elastic recoil detection analysis (HI-ERDA). Samples were deposited from SiH_(4), O_(2), and N_(2) gas mixtures, with different gas flow ratios in order to obtain compositions ranging from SiN_(y)H_(z) to SiO_(2). Those samples deposited at higher SiH_(4) partial pressures show both Si-H and N-H bonds, while those deposited at lower SiH_(4) 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 SiO_(x)N_(y) 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.