Thermodynamics of the production of condensed phases in the CVD process of B_xC with BCl₃-C₃H₆ (propylene)-H₂ precursors

The temperature, pressure and the molar ratio of the injected gas mixture for the deposition of the condensed phases in the CVD process of B_xC with BCl₃-C₃H₆(propylene)-H₂ precursors are investigated in detail thermodynamically with a revised database including 329 species. The results show that the composition of the condensed phases is quite sensitive to both temperature and the molar ratios of BCl₃/(BCl₃+C₃H₆) and H₂/(BCl₃+C₃H₆) while it is less sensitive to pressure. The ideal conditions for the deposition of B_xC are BCl₃/(BCl₃+C₃H₆) ratio within 0.88~0.92, H₂/(BCl₃+C₃H₆) ratio within 10~10^5.2 and temperature above 1100 K at lower pressures. The co-deposition of C or B with B_xC is mainly controlled by the ratios of BCl₃/(BCl₃+C₃H₆) and H₂/(BCl₃+C₃H₆). The co-deposition of C with B_xC should be in low BCl₃/(BCl₃+C₃H₆) (0.0~0.88) and H₂/(BCl₃+C₃H₆) (10^-2<10^2.4) ratios while the co-deposition of B with B_xC needs higher BCl₃/(BCl₃+C₃H₆) (0.92~1.0) and H₂/(BCl₃+C₃H₆) (10⁴~10⁵) ratios.