We have investigated the growth of microcrystalline silicon(μc-Si) films using ECR plasma CVD with varying substrate temperature, Ts, and dilution ratios [i.e. $H_2$/($SiH_4$+$H_2$)] of the excitation gases such as hydrogen and helium. The structural properties of the films, i. e., crystalline volume fraction and the orientation of the crystallites, are examined by Raman scattering and x-ray diffraction spectroscopy. In case of hydrogen dilution ratio 0.5, the dominant phases of the films change from amorphous to microcrystalline in the substrate temperature range between 130℃ and 500℃. But dilution ratios exceed 0.9, the crystalline volume fractions of the films continuously increase with substrate temperature and reach above 90% at 550℃. Interestingly, the deposition rate increases abruptly with substrate temperature above 400℃ under high hydrogen dilution ratios above 0.9.
Further, XRD spectroscopy reveal that a (110)-oriented growth of the crystallites. However, in this case, as the gas pressure increases, the structure of the films changes from microcrystalline to amorphous phase. When using helium gas, the phase transition of deposited silicon films show similar dependence on substrate temperature, dilution ratios as in the case of hydrogen dilution. It is worth noting that these results are very different with those of PECVD in which microcrystalline silicon films does not form at substrate temperatures of above 450℃. This effect might be understood by considering the role of high density ions or metastable exciting gas generated by ECR that promote surface diffusion of adsorption precusors on the growing surface of the silicon films. Finally, hydrogenated amorphous silicon thin films of device quality can be obtained under deposition pressure of 100 mTorr. In particular, with substrate temperature of 350℃ and the flow rate of $SiH_4$:$H_2$ = 5 sccm : 60 sccm, a more stable films against light soaking can be deposited.
