CORRELATION AMONG SI, GE, AND B DEPOSITION RATES IN LOW-PRESSURE CVD WITH SIH4-GEH4-B2H6-HE MIXTURES

The deposition process at 500-degrees-C with SiH4-GeH4-B2H6-He mixtures, which yields the amorphous Si-Ge-B alloy, was studied. Although in crystalline Si and Ge the maximum B content is limited to the solid solubility, any amount of B can uniformly be contained in amorphous Si-Ge-B. Thus, films with a B content up to 64 at. % have been prepared. The deposition rate of atoms, defined as the number of atoms deposited in a unit time interval, is obtained for each element by analyzing the growth rate together with the composition and the mass density of the film. When the SiH4 and the B2H6 partial pressures are constant, the Si and the B deposition rates are almost independent of the GeH4 partial pressure. In contrast, the Si deposition rate increases remarkably as the B2H6 partial pressure increases, even when the SiH4 partial pressure is maintained constant. A simple model is proposed for explaining the relationship between the Si and the B deposition rates.