KINETICS OF CHEMICAL-VAPOR-DEPOSITION OF BORON-NITRIDE FROM A GAS-MIXTURE OF TRIMETHYLBORAZINE, AMMONIA, AND HYDROGEN AT 900-TO-1050-DEGREES-C AND 1-BAR TOTAL PRESSURE

The kinetics of CVD of boron nitride from a gas mixture of 1,3,5-tri(N -methyl)borazine (TMB), ammonia, and hydrogen were studied at 900 to 1 050 degrees C and a total pressure of 1 bar. TMB, a liquid between -3 and 136 degrees C, is assumed to be a single source precursor for CVD of BN. However, to suppress gas phase nucleation, one has to add suffi ciently large amounts of ammonia. Below 900 degrees C no deposition wa s observed within 10 hours. Between 900 and 980 degrees C the depositi on rate was controlled by a surface reaction with an apparent activati on energy of 145 kJ mol(-1). The reaction was found to be first-order with respect to TMB and zero-order in both NH3 and H-2. Above 1000 deg rees C the activation energy decreased to 26 kJmol(-1) which correspon ds to gas diffusion as the rate-determining step. Gas phase nucleation makes it difficult to produce smooth films above 1000 degrees C. The reaction product was turbostratic hexagonal boron nitride with about 5 2 at.-% nitrogen, 46 at.-% boron, and 1-2 at.-% codeposited carbon.