Chemical vapour deposition of silicon under reduced pressure in a hot-wall reactor: Equilibrium and kinetics

Silicon chemical vapour deposition (SiH2Cl2/H2 system), under reduced pressure conditions, in a hot-wall reactor, is presented. The vapour phase composition is assessed by evaluating two distinct equilibria. The homogeneous equilibrium , which assumes that the vapour phase is not in equilibrium with solid silicon, is thought to give an adequate description of the vapour phase in the case of low pressure, high gas velocities, good temperature homogeneity conditions. A comparison with heterogeneous equilibrium enables us to calculate the supersaturation so evidencing a highly irreversible growth system. The experimental determination of the growth rates reveals two distinct temperature ranges: below 10000C, polycrystalline films are usually obtained with a thermally activated growth rate (+40 kcal mole-1) and a reaction order, with respect to the predominant species SiCl2, close to one; above 10000C, the films are always monocrystalline and their growth rate exhibits a much lower or even negative activation energy, the reaction order in SiCl2 remaining about one. (orig.)