Effect of C and Ge concentration on the thermal stability of RTCVD grown Si1-x-yGexCy alloys

Si / Si1-x-yGexCy / Si heterostructures containing up to 17 at.% Ge and 1.9 at.% C were grown on (001) silicon by low pressure Rapid Thermal Chemical Vapor Deposition, using a mixture of silane, germane and methylsilane, diluted in hydrogen. The samples were then annealed in a Rapid Thermal Processing furnace, under an atmospheric pressure of nitrogen, at temperatures ranging from 900 to 1130 degrees C. The samples were characterized using infrared spectroscopy and x-ray diffraction. SIMS profiling and TEM observation were performed on some of the samples. Substitutional C gradually disappeared, either precipitating out to form cubic silicon carbide (beta-SiC), or simply vanishing into interstitial positions. In any case, the in-plane lattice constant remained constant after annealing, indicating that there was no mechanical strain relaxation by formation of misfit dislocations. The perpendicular lattice constant increased due to the decrease in substitutional C concentration, as well as it decreased due to the germanium out-diffusion. This variation of the strain during annealing was modeled, and allowed the determination of the kinetics of the substitutional carbon disappearance. The same behavior was observed for all samples. Indeed, the C-S disappearance rate was always increased for samples with higher initial Ge and C concentrations. The kinetics of this precipitation was found in very good agreement with previous published results.