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=800 °C), 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.