Potential Precursor Alternatives to the Pyrophoric Trimethyl Aluminum for the Atomic Layer Deposition of Aluminum Oxide.

New precursor chemistries for the ALD of Al₂O₃ are reported as potential alternatives to the pyrophoric trimethylaluminum which is till date a widely used Al precursor. Combining the high reactivity of aluminum alkyls employing the 3- (dimethylamino)propyl (DMP) ligand with thermally stable amide ligands yielded three non-pyrophoric compounds [Al(NMe₂)₂(DMP)] , [Al(NEt₂)₂(DMP)] (BDEADA) and [Al(NiPr₂)₂(DMP)] that unify the properties of both ligand systems. The compounds are intramolecular stabilized and show only reactive Al-C and Al-N bonds, which are the key factors for the thermal stability accompanied by a sufficient reactivity. Upon rational variation of the amide alkyl chains, tunable and high evaporation rates accompanied by thermal stability were found as revealed by thermal evaluation. Additionally, a new and promising plasma enhanced (PE)ALD process using BDEADA and O₂ plasma in a wide temperature range from 60 to 220 °C is reported and compared to that of a modified variation of the TMA, namely [AlMe₂(DMP)] (DMAD). The resulting Al₂O₃ layers are of high density, smooth, uniform and of high purity. The applicability of the Al₂O₃ films as effective gas barrier layers was successfully demonstrated wherein coating on polyethylene terephthalate substrates yielded very good oxygen transmission rates. All these film attributes are of the same quality as those obtained for the industrial precursor TMA rendering the new precursors as safe and potential alternatives to TMA.