Deposition process of W onto a-Si:H observed in-situ with polarization modulation IR and quadrupole mass spectroscopies

The reaction processes of WF₆ with photochemically deposited a-Si:H films were studied in situ by polarization modulation IR spectroscopy and quadrupole mass spectrometry. The IR bands due to the hydrogenated silicon species (-SiH₃ and -SiH₂) incorporated in the film decreased in intensity during the exposure to WF₆. Irrespective on the exposure temperature, the intensity reduction rates of the -SiH₃ species were much larger than those of the -SiH₂ species. Gas-phase analysis revealed that the evolution of hydrogen into the gas phase took place prior to that of silicon fluorides. Inductively coupled plasma analysis showed that the weight of W deposited on the substrate increased steeply just after the beginning of the exposure, then tended to be saturated beyond the exposure time at which the IR bands due to the -SiH₃ species almost disappeared. These results indicate that WF₆ reacts preferentially with the -SiH₃ species present in the hydrogen-rich surface layer and further deposition reaction is strongly suppressed by the W layer formed on the surface.