Plasma CVD of hydrogenated boron-carbon thin films from triethylboron

Low-temperature chemical vapor deposition (CVD) of B-C thin films is of importance for neutron voltaics and semiconductor technology. The highly reactive trialkylboranes, with alkyl groups of 1-4 carbon atoms, are a class of precursors that have been less explored for low-temperature CVD of B-C films. Herein, we demonstrate plasma CVD of B-C thin films using triethylboron (TEB) as a single source precursor in an Ar plasma. We show that the film density and B/C ratio increases with increasing plasma power, reaching a density of 2.20 g/cm³ and B/C = 1.7. This is attributed to a more intense energetic bombardment during deposition and more complete dissociation of the TEB molecule in the plasma at higher plasma power. The hydrogen content in the films ranges between 14 and 20 at. %. Optical emission spectroscopy of the plasma shows that BH, CH, C₂, and H are the optically active plasma species from TEB. We suggest a plasma chemical model based on β-hydrogen elimination of C₂H₄ to form BH₃, in which BH₃ and C₂H₄ are then dehydrogenated to form BH and C₂H₂. Furthermore, C₂H₂ decomposes in the plasma to produce C₂ and CH, which together with BH and possibly BH_3-x(C₂H₅)_x are the film forming species.