CHEMICAL VAPOR DEPOSITION OF TiB2 FOR TiN-TiB2 LAMINAR COMPOSITES

TiB₂ is a material with very interesting properties with respect to erosion and corrosion resistance. Deposition on metallic substrates using TiCI₄, BBr₃ or BCI₃ and H₂ at temperatures around 900° C results in coronation of the substrate, which is most severe when using BBr₃. Therefore, a TiN diffusion barrier is applied. Here we discuss the deposition of TiB₂ using BCI₃ on molybdenum and TiN and compare the results with those of the thermodynamically more favorable reaction with BBr₃. Smooth TiB₂ layers are formed when using BCI₃, with faceting occurring above 900° C. The morphology seems to be independent of the BCI₃/TiCl₄ ratio in the gas phase for values between 0·5 and 4. With an excess of boron in the gas phase - BCI₃/TiCl₄ = 8, depletion occurs already at 800° C. An apparent activation energy of 210 KJ/mol has been determined for a stoichiometric gas phase with BCl₃/TiCI₄ = 2. When the supply of boron is limiting - BCl₃/TiCl₄ = 0·5, the activation energy is 120 KJ/mol.