EFFECTS OF WATER-VAPOR AND CHLORINE ON THE EPITAXIAL-GROWTH OF SI1-XGEX FILMS BY CHEMICAL-VAPOR-DEPOSITION - THERMODYNAMIC ANALYSIS

The effects of water vapor and chlorine on the Si1-xGex epitaxial grow th are studied through thermodynamic analyses. Since Ge does not form chemical species with oxygen at an appreciable level, the water vapor and oxygen background level requirements for Si1-xGex epitaxial growth are mostly similar to the ones for Si growth. At large excesses of Ge gas phase sources and low system water vapor level, however, the crit ical temperature above which oxide-free epitaxial growth occurs decrea ses with increasing system pressure. Analyses of the results obtained suggest that there are two mechanisms for the removal of SiO2(s) from the surface: one is by forming volatile SiO, and the other is by formi ng gas phase H2O. The former one appears to dominate for most conditio ns studied; the latter one appears to dominate when the water vapor le vel of the system is very low and/or small amounts of the Si gaseous s ource are present. The boundary between etching and deposition of Si1- xGex films is examined for all Ge solid phase compositions. The etch/d eposition boundaries for pure Si and pure Ge show opposite trends with increasing chlorine concentrations, because of the different affiniti es of Si and Ge to form chlorinated species. The chlorine concentratio n needed to reach etching increases with increasing system temperature for Si, whereas it decreases with increasing temperature for Ge. It i s found that the formation of SiCl4 is favored over GeCl2 at low tempe ratures, while the opposite happens at higher temperatures. The etch/d eposition boundary for Si1-xGex thin films is found to form a saddleli ke contour because of the interaction of the different behaviors of Si and Ge. Overall, calculated results are seen to be in good agreement with available experimental results. (C) 1997 American Vacuum Society.