Atomic layer deposition of BN as a novel capping barrier for B2O3

The deposition of boron oxide (B2O3) films on Si and SiO2 substrates by atomic layer deposition (ALD) is of growing interest in microelectronics for shallow doping of high aspect ratio transistor structures. B2O3, however, forms volatile boric acid (H3BO3) upon ambient exposure, requiring a passivation barrier, for which BN was investigated as a possible candidate. Here, the authors demonstrate in situ deposition of BN by sequential BCl3/NH3 reactions at 600K on two different oxidized boron substrates: (a) B2O3 deposited using BCl3/H2O ALD on Si at 300K (B2O3/Si) and (b) a boron-silicon oxide formed by sequential BCl3/O-2 reactions at 650K on SiO2 followed by annealing to 1000K (B-Si-oxide). X-ray photoelectron spectroscopy (XPS) data demonstrate layer-by-layer growth of BN on B2O3/Si with an average growth rate of similar to 1.4 angstrom/cycle, accompanied by some B2O3 removal during the first BN cycle. In contrast, continuous BN growth was observed on B-Si-oxide without any reaction with the substrate. XPS data also indicate that the oxide/nitride heterostructures are stable upon annealing in ultrahigh vacuum to >1000K. XPS data, after the exposure of these heterostructures to ambient, indicate a small amount of BN oxidation at the surface NHx species, with no observable hydroxylation of the underlying oxide films. These results demonstrate that BN films, as thin as 13 angstrom, are potential candidates for passivating boron oxide films prepared for shallow doping applications.