Real-time IR and mass spectroscopic study of the reaction process of WF₆ and a-Si:H:F

The deposition process of W from WF₆ onto a-Si:H:F film was studied by polarization modulation IR spectroscopy combined with quadruple mass spectrometry. The IR spectrum of the a-Si:H:F film formed by the spontaneous chemical deposition method (deposition temperature 373 K) showed that such fluorinated and hydrogenated Si species as -SiF₂, -SiF₂H and -SiH₂ were incorporated in the film. The lowest temperature at which W was deposited was 403 K. The intensity reduction of the IR bands due to the hydrogenated and fluorinated Si species as well as the evolutionary behaviour of the reaction products SiF₄ and H₂ depended upon the reaction temperature. At temperature between 403 K and 423 K, the IR band intensity of the -SiH₂ species remained unchanged in early stages of WF₆ exposure, while the bands due to -SiF₂ and -SiF₂H species decreased linearly with exposure time. No evolution of H₂ was observed as long as the -SiH₂ species remained unchanged, through SiF₄ evolved into the gas phase just after the beginning of the exposure. These results suggest that WF₆ reacts preferentially with the fluorinated silicon species in the films.