Microstructure characterization of amorphous thin solid films in a fringe-free environment

We have comprehensively analyzed the influence of the probe beam's polarization state and incident angle on the vibrational absorption spectra of thin solid films such as hydrogenated amorphous silicon nitride and hydrogenated amorphous silicon in Fourier transform infrared spectroscopy. This analysis demonstrates the nuisance of interference fringes in distorting the bond structure of thin solid films in conventional vibrational absorption spectra. Based on the spectrum analysis and optical fundamentals, a practical method of recording a vibrational absorption spectrum of a thin solid film in an interference fringe-free environment is proposed. Furthermore, it is also demonstrated that a fringe-free spectrum can be recorded even in an interference-embedded environment if a right light incident angle is chosen. This interference-embedded fringe-free spectrum is only valid for material's qualitative microstructure assessment but not for direct quantitative analysis. Finally, a comparison between ideal spectra and those fringe-corrected by conventional measures indicates a nontrivial discrepancy. Therefore, only interference-free spectrum exhibits the absolute features of the bond structures, and should be the standard spectrum used for thin solid film microstructure assessment. (C) 1999 American Institute of Physics. [S0021-8979(99)00401- 6].