Microstructural and microtextural investigations of boron nitride deposited from BCl3-NH3-H2 gas mixtures

The structural, morphological and textural characteristics of BN coatings processed by CVD from (BCl3, NH3, H2) gas mixtures, at low pressure (P=1.3 kPa) and low temperature (T=800NBDGC), with different QNH3/QBCl3 gas flow rate ratios, have been investigated. Whereas the as-processed coatings are amorphous, a high degree of crystallisation can be achieved after a post-deposition heat treatment. The sole post-elaboration heat treatment does not allow the improvement of the crystallisation degree of the boron nitride. The presence of a small amount of oxygen, resulting from a simple exposure of the coating to a controlled atmosphere (temperature, moisture rate), is also necessary. For given temperature and pressure, a wide range of microstructures of the heat-treated BN coatings, from isotropic to anisotropic, can be observed by varying the QNH3/QBCl3 ratio.