SIMULTANEOUS CHEMICAL VAPOR-DEPOSITION OF BORON-NITRIDE AND ALUMINUM NITRIDE

Two chemically different phases, hexagonal BN and AlN, were simultaneously produced by chemical vapor deposition (CVD) using an impinging jet reactor and the BCl3-AlCl3-NH3-Ar reagent system. The microstructure of the BN + AlN composite coatings was strongly dependent on temperature, pressure, and BCl3 and AlCl3 concentrations. The growth characteristics of BN and AlN in the codeposition system were similar to those expected from the single-phase deposition processes (i.e., BN-CVD and AlN-CVD), except the growth of AlN whiskers was accentuated, and competition between BN and AlN deposition in the composites was suspected to be the cause of less-crystalline deposits. In both BN + AlN-CVD and AlN-CVD, the growth of AlN whiskers became more apparent with increasing pressure or temperature. The codeposition behavior observed experimentally was compared with thermodynamic predictions.