DEPOSITION OF BORON-CARBIDE BY LASER CVD - A COMPARISON WITH THERMODYNAMIC PREDICTIONS

Thin films in the boron-carbon system have been deposited by CO2 laser chemical vapour deposition (LCVD) on fused silica plates from a gas m ixture of BCl3, CH4, H-2 and Ar. Glancing incidence X-ray diffraction (GIXRD) and electron-probe microanalysis (EPMA) were extensively used for characterisation of structure and chemical composition, respective ly. Depending on the process parameters, three different phases were d eposited: rhombohedric boron carbide and graphite (stable phases), and a metastable tetragonal boron rich carbide. Thermodynamic calculation s were performed for a broad range of gas phase compositions and the d ata obtained were compared to the experimental results. This compariso n showed a generalised lack of carbon (or excess of boron) in all the deposited films and was also used to estimate the deposition temperatu re. (C) 1997 Elsevier Science S.A.