Evolution of structure in thin microcrystalline silicon films grown by electron-cyclotron resonance chemical vapor deposition

The growth of microcrystalline silicon, $\mathrm{\mu c-}\mathrm{Si},$ films has been studied by infrared spectroscopy and x-ray diffraction. Thin films of various thickness have been prepared from ${\mathrm{SiH}}_{\mathrm{4}}{\mathrm{–H}}_{\mathrm{2}}$ mixtures by electron-cyclotron resonance chemical vapor deposition. Two structural transitions were observed during film growth. The first transition at a critical thickness of $d_{\mathrm{ac}}\text{=9\hspace{0.05em}}\mathrm{nm}$ manifested itself by a change from an initially amorphous growth to polycrystalline growth. The second structural transition was related to an increasing amount of silicon grains of preferred orientation with (110) lattice planes parallel to the substrate. The population of such (110)-oriented grains $N_{110}$ was found to become dominant at about $d_{110}\text{=310\hspace{0.05em}}\mathrm{nm},$ which may be considered as a second critical thickness above which the film exhibits a (110) fiber texture. The increase of $N_{110}$ with increasing thickness follows a $d^{\text{1/6}}$ dependence. The effect is understood in terms of an interplay between etching and deposition during growth.