Potential Precursor Alternatives to the Pyrophoric Trimethylaluminium for the Atomic Layer Deposition of Aluminium Oxide

Abstract

New precursor chemistries for the atomic layer deposition (ALD) of aluminium oxide are reported as potential alternatives to the pyrophoric trimethylaluminium (TMA) which is to date a widely used Al precursor. Combining the high reactivity of aluminium alkyls employing the 3‐(dimethylamino)propyl (DMP) ligand with thermally stable amide ligands yielded three new heteroleptic, non‐pyrophoric compounds [Al(NMe2)2(DMP)] (2), [Al(NEt2)2(DMP)] (3, BDEADA) and [Al(NiPr2)2(DMP)] (4), which combine the properties of both ligand systems. The compounds were synthesized and thoroughly chemically characterized, showing the intramolecular stabilization of the DMP ligand as well as only reactive Al−C and Al−N bonds, which are the key factors for the thermal stability accompanied by a sufficient reactivity, both being crucial for ALD precursors. Upon rational variation of the amide alkyl chains, tunable and high evaporation rates accompanied by thermal stability were found, as revealed by thermal evaluation. In addition, a new and promising plasma enhanced (PE)ALD process using BDEADA and oxygen 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 (GBLs) was successfully demonstrated, considering that coating on polyethylene terephthalate (PET) substrates yielded very good oxygen transmission rates (OTR) with an improvement factor of 86 for a 15 nm film by using DMAD and a factor of 25 for a film thickness of just 5 nm by using BDEDA compared to bare PET substrates. All these film attributes are of the same quality as those obtained for the industrial precursor TMA, rendering the new precursors safe and potential alternatives to TMA.

From Precursor Chemistry to Gas Sensors: Plasma‐Enhanced Atomic Layer Deposition Process Engineering for Zinc Oxide Layers from a Nonpyrophoric Zinc Precursor for Gas Barrier and Sensor Applications

“…[ 67 ] Of course, for the ZnO layers obtained herein, this needs to be proven and is currently under investigation. However, the barrier performance is in the same range as the OTR of equivalently thick Al 2 O 3 layers on PET, as shown earlier for the same polymer substrates, [ 49,50 ] rendering the ZnO layers to be applicable as transparent gas barrier layers (GBLs).…”

“…Recently we successfully demonstrated that intramolecular stabilized aluminum compounds can potentially substitute trimethyl aluminum (TMA), which is virtually the DEZ equivalent of aluminum precursors. [ 49,50 ] This approach was adapted toward zinc compounds which is the focus of this study for ALD applications. Thus, bis‐3‐( N , N ‐dimethylamino)propyl zinc(II) ([Zn(DMP) 2 ], BDMPZ) was synthesized by introducing the 3‐( N , N ‐dimethylamino)propyl (DMP) ligand which stabilizes the Zn center via a dative bond of the amine, [ 51,52 ] and thoroughly analyzed the compound in terms of its thermal properties.…”

An Easy, Convenient, and Safe Process for the Synthesis of Lofexidine Hydrochloride

“…Unfortunately, trimethylaluminum is pyrophoric and reacts violently with water or moisture in the atmosphere, generating methane . The use of this reactant on a production scale would be rather complex and would require some economical investments to implement a proper system to mitigate hazards related to the handling of the substance and its flammable byproducts.…”

“…We found another interesting paper, reporting a one-pot reaction of alkylated phenols (of general formula 10) with ethylenediamine (5) in the presence of trimethylaluminum. 9,10 The reaction is carried out in toluene at reflux and gives access to imidazoline rings (11) in a very high molar yield (>90%) (Scheme 3).…”

Green CVD—Toward a sustainable philosophy for thin film deposition by chemical vapor deposition

“…TMA is pyrophoric and will self-ignite in contact with air making it very unsafe to use without very stringent and expensive installations on the precursor delivery side as well as in the abatement system. Despite, but partly due to, the widespread use of TMA, accidents with smaller or larger fires with TMA are common in the CVD facilities using precursors 35 , AlCl3 seems to emerge as a serious contender to replace TMA for some applications. 36 AlCl3 is a solid and has been successfully used in the hard metal coating industry for hard, high-temperature oxidation protection of cemented carbide tool bits.…”