EQUILIBRIUM THERMODYNAMIC ANALYSIS OF THE SI-GE-CL-H SYSTEM FOR ATMOSPHERIC AND LOW-PRESSURE CVD OF SI1-XGEX

Thermodynamic equilibrium calculations have been performed for the Si-Ge-Cl-H system for both atmospheric and low pressure CVD of Si1-xGex under various conditions. The equilibrium compositions of the deposited layers and their dependence on temperature, pressure and chlorine-to-hydrogen ratio were determined. The calculation results show that the deposit composition tends to be enriched in the Ge component at low temperature, high pressure and large Cl/H. Two gas sources where examined. The equilibrium compositions were found to be less sensitive to growth parameters for SiH2Cl2 + GeH4 + H-2 than for SiCl4 + GeCl4 + H-2. Equilibrium deposition efficiencies have also been calculated as a function of the pressure and Ge concentration. The calculated and the experimental results show agreement in the high temperature range. At lower temperatures. a significant increase of growth rate with increasing Ge content experimentally observed by several authors. seems to be a kinetic auto-catalytic effect instead of a thermodynamic property.