The reaction of dimethylaluminum hydride (DMAH) with a-Si:H:F films prepared by spontaneous chemical vapor deposition (SCVD) has been studied in situ using polarization modulation IR spectroscopy. It is found that SCVD films before DMAH exposure contain SiF 2 , SiH 2 , and SiH 2 species. Upon exposure to DMAH at a temperature ranging from 373 to 593 K, the IR bands due to SiF 2 and SiH 2 F stretch vibrations decrease in intensity, whereas the intensity of the SiH 2 stretch band increases. These changes are remarkable at high temperature; in particular the SiH 2 stretch band shifts to lower wavenumber with increasing exposure temperature. These results suggest that DMAH reacts with the SiF 2 and SiH 2 F species to form SiH 2 and SiH 3 . We also reveal a temperature dependent correlation between the spectral changes and the deposited amounts of Al, as determined by induced coupled plasma analysis.