Kinetics of Chemical Vapour Deposition of Boron Nitride from a Gas Mixture of Trimethylborazine, Ammonia, and Hydrogen at 900 to 1050 °C and 1 Bar Total Pressure

Abstract
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 1050°C and a total pressure of 1 bar. TMB, a liquid between -3 and 136°C, is assumed to be a single source precursor for CVD of BN. However, to suppress gas phase nucleation, one has to add sufficiently large amounts of ammonia. Below 900°C no deposition was observed within 10 hours. Between 900 and 980°C the deposition rate was controlled by a surface reaction with an apparent activation 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 H₂. Above 1000°C the activation energy decreased to 26 kJmol^-1 which corresponds to gas diffusion as the rate-determining step. Gas phase nucleation makes it difficult to produce smooth films above 1000°C. The reaction product was turbostratic hexagonal boron nitride with about 52 at.-% nitrogen, 46 at.-% boron, and 1-2 at.-% codeposited carbon.