FTIR phase-modulated ellipsometry measurements of microcrystalline silicon films deposited by hot-wire CVD

A series of thin silicon films has been prepared by hot-wire CVD (HWCVD), varying the dilution of silane SiH4 in hydrogen H2, defined as the flow ratio [H2]/([H2]+[SiH4]), from 0.88 to 0.98. The microstructure of the films has been observed to evolve from the amorphous to the microcrystalline phase, with the increase of the dilution. The aim of this paper has been to correlate the changes of silicon–hydrogen bond configurations of the films with the microstructure evolution. The structural evolution of the films was assessed by Raman spectroscopy while the silicon–hydrogen bond evolution was analyzed by FTIR phase-modulated ellipsometry. Thus, the silicon–hydrogen absorption band, in the range 2000–2100 cm−1, was deconvoluted into two main contributions due to the SiH and SiH2 stretching vibration modes. For low dilutions (<0.92), ascribed to the amorphous phase, the SiH bond configuration has been found to co-exist with the bulk SiH2 configuration, whereas for high dilution (0.98), assigned to microcrystalline phase, only the surface SiH2 mode has been observed. A non-abrupt transition has been occurring between both phases.