Thermodynamic calculations for the chemical vapor deposition of hexagonal boron nitride using triethylboron, ammonia, and hydrogen

Abstract

The presence of C in B(C2H5)3 makes possible its incorporation into hexagonal boron nitride (h-BN) thin films grown during chemical vapor deposition (CVD) under select process conditions. A series of CVD phase diagrams that indicate the regions of stability of the phases of h-BN, C and B4C as a function of temperature and input mole ratio of reactants (N/B) under set pressures and H2 diluent-to-reactant mole ratios (H2/(B + N)) have been calculated and analyzed for the TEB/NH3/H2 system. The equilibrium calculations showed that within the total pressure range of 0.01-100 Torr, increasing the H2 content in the TEB/NH3/H2 gas mixture tends to suppress the stability of C throughout a 400–1600 °C temperature range, but it also suppresses the stability of h-BN at higher temperatures. Further, it was determined that increasing the total system pressure suppresses the occurrence of C as a second phase while expanding the stability of h-BN. The thermodynamic equilibrium results were compared to the results of experimental investigations involving the CVD synthesis of sp2-BN as a means to evaluate their usefulness as a guide for avoiding the co-deposition of C and B4C with h-BN.