A kinetic model for Si1-x gex growth from Si H4 and Ge H4 by CVD

A kinetic model is proposed for silicon-germanium alloy (Si1-x Gex) growth from silane (Si H4) and germane (Ge H4) by chemical vapor deposition. It takes into account both homogeneous and heterogeneous reactions, which involve the precursors (Si H4 and Ge H4) and the homogeneous decomposition product of germane, germylene (Ge H2), and three types of surface sites: silicon sites, hydrogen-terminated silicon sites, and germanium sites. The growth of Si1-x Gex can be divided into two regimes: a heterogeneous decomposition dominated regime and a homogeneous decomposition dominated regime. For the heterogeneous regime, analytical equations based on the collision theory of heterogeneous unimolecular reactions, statistical physics, and the concept of competitive adsorption are derived to quantitatively describe growth rate and film composition as a function of deposition conditions, including deposition temperature, silane flow rate, and germane flow rate. Homogeneous decomposition of germane into germylene complicates the gas phase chemistry for both germane and silane, and an empirical linear relation is employed to describe the growth behavior in the homogeneous regime. The model agrees well with the experimental data by Jang [J. Electrochem. Soc. 142, 3513 (1995)].