Effect of C/B ratio in reactants on low-pressure CVD boron-doped carbon deposited from a BCl₃-C₃H₆-H₂ mixture

Propylene was used to fabricate boron-doped carbon coatings by low-pressure chemical vapor deposition. The effects of carbon/boron (C/B) ratio in reactants on the deposition rate, morphologies, and bonding states of the deposits were investigated. Deposition rate increased with increasing C/B ratio, when C/B ratio was less than 4.0. Then, deposition rate decreased with increasing C/B ratio. The maximum rate was 500 nm/h. SEM results showed that cross section morphologies and thickness of deposits were influenced by C/B ratio. Morphologies were compact and not-delaminated with a low C/B ratio, however nanoscale delamination occurred in the deposits with a high C/B ratio. The infiltration characteristic was also influenced by the C/B ratio. The suitable C/B ratio was 1.0-2.0 for infiltration in a T300 carbon bundle. XPS results showed that carbon content is major in the deposits with all C/B ratios. The boron contents decreased and carbon contents increased with increasing C/B ratio. B-sub-C and BC₂O were main bonding states. The total contents of B-sub-C and BC₂O were above 60.0 at.% with all C/B ratios.