Kinetics of hydrogen in preparing amorphous B₅C:H thin films

The kinetics of hydrogen in preparing amorphous boron carbide (a-B ₅C:H) thin films was studied. The hydrogen concentration of a-B5C:H thin films formed by plasma-enhanced chemical vapor deposition (PECVD) from a single-source precursor (o-B₁₀C₂H₁₂) is ∼35-50 at.% as determined by nuclear reaction analysis. The hydrogen concentration of the a-B5C:H thin films is an exponential function of the precursor flux during the deposition. After annealing, the hydrogen concentration in the a-B5C:H thin films decreases with the increasing annealing temperature. The kinetics of hydrogen removal during annealing is controlled predominantly by its dissociation from PECVD radicals in the a-B5C:H thin films. The activation energy of about 0.14 eV is related to hydrogen dissociation from B-H bonds, but higher activation energy (∼0.44 eV) is required to strip the hydrogen atoms from C-H bonds in the thin films.