Resolving Impurities in Atomic Layer Deposited Aluminum Nitride through Low Cost, High Efficiency Precursor Design.

A heteroleptic amidoalane precursor is presented as a more suitably designed candidate to replace trimethylaluminum (TMA) for atomic layer deposition of aluminum nitride (AlN). The lack of C-Al bonds and the strongly reducing hydride ligands in [AlH2(NMe2)]3 (1) were specifically chosen to limit impurities in target aluminum nitride (AlN) films. Compound 1 is made in a high yield, scalable synthesis involving lithium aluminum hydride and dimethylammonium chloride. It has a vapor pressure of 1 Torr at 40 °C and evaporates with negligible residual mass in thermogravimetric experiments. Ammonia (NH3) plasma and 1 in an atomic layer deposition (ALD) process produced crystalline AlN films above 200 °C with an Al:N ratio of 1.04. Carbon and oxygen impurities in resultant AlN films were reduced to <1% and <2%, respectively. By using a precursor with a rational and advantageous design, we can improve the material quality of AlN films compared to those deposited using the industrial standard trimethylaluminum and could reduce material cost by up to 2 orders of magnitude.

Synthesis and Thermal Study of Hexacoordinated Aluminum(III) Triazenides for Use in Atomic Layer Deposition.

Amidinate and guanidinate ligands have been used extensively to produce volatile and thermally stable precursors for atomic layer deposition. The triazenide ligand is relatively unexplored as an alternative ligand system. Herein, we present six new Al(III) complexes bearing three sets of a 1,3-dialkyltriazenide ligand. These complexes volatilize quantitatively in a single step with onset volatilization temperatures of ∼150 °C and 1 Torr vapor pressures of ∼134 °C. Differential scanning calorimetry revealed that these Al(III) complexes exhibited exothermic events that overlapped with the temperatures of their mass loss events in thermogravimetric analysis. Using quantum chemical density functional theory computations, we found a decomposition pathway that transforms the relatively large hexacoordinated Al(III) precursor into a smaller dicoordinated complex. The pathway relies on previously unexplored interligand proton migrations. These new Al(III) triazenides provide a series of alternative precursors with unique thermal properties that could be highly advantageous for vapor deposition processes of Al containing materials.