Thermodynamic model of nucleation and growth of plasma deposited microcrystalline silicon

Hydrogen dilution is used to promote the nucleation and growth of microcrystalline Si (μc–Si) by plasma-enhanced chemical-vapor deposition. The free energy of μc–Si and hydrogenated amorphous silicon (a–Si:H) is analyzed as a function of the Si:H composition in order to understand the effect of hydrogen dilution. It is shown that increasing the hydrogen content of the a−SiHx precursor phase increases the relative stability of μc–Si slightly, but strongly increases the driving force for nucleation. The higher stability of μc–Si is the fundamental origin of the higher etch rates of a–Si:H, while surface mobility models do not account for subsurface nucleation of μc–Si.