Structural model of sputtered fluorinated amorphous silicon

Structure of a fluorinated amorphous-silicon alloy (a-Si:F), which is produced by the sputtering of Si in mixtures of Ar and SiF4 gases, is studied by transmission electron microscope (TEM). As a special technique to study the localization of both atomic species and particular types of Si-F configuration, the change of TEM micrograph due to anisotropic chemical etching of samples is observed, and it is compared with the similar changes in infrared absorption spectra and the Rutherford backscattering spectra. The evolved gases from heated a-Si:F are also analyzed to determine the role of Ar atoms in the microstructure. It is found that a-Si:F film consists of many small grains of a-Si network, and that both Si-F4 bonds and Ar atoms are localized at the grain boundary. Based on these results, the most possible structural model for a-Si:F, which suggests key factors to improve the properties, is presented.