Aluminum dihydride complexes and their unexpected application in atomic layer deposition of titanium carbonitride films

Abstract

Aluminum dihydride complexes containing amido-amine ligands were synthesized and evaluated as potential reducing precursors for thermal atomic layer deposition (ALD). Highly volatile monomeric complexes AlH₂(tBuNCH₂CH₂NMe₂) and AlH₂(tBuNCH₂CH₂NC₄H₈) are more thermally stable than common Al hydride thin film precursors such as AlH₃(NMe₃). ALD film growth experiments using TiCl₄ and AlH₂(tBuNCH₂CH₂NMe₂) produced titanium carbonitride films with a high growth rate of 1.6–2.0 Å per cycle and resistivities around 600 μΩ cm within a very wide ALD window of 220–400 °C. Importantly, film growth proceeded via self-limited surface reactions, which is the hallmark of an ALD process. Root mean square surface roughness was only 1.3% of the film thickness at 300 °C by atomic force microscopy. The films were polycrystalline with low intensity, broad reflections corresponding to the cubic TiN/TiC phase according to grazing incidence X-ray diffraction. Film composition by X-ray photoelectron spectroscopy was approximately TiC_0.8N_0.5 at 300 °C with small amounts of Al (6 at%), Cl (4 at%) and O (4 at%) impurities. Remarkably, self-limited growth and low Al content was observed in films deposited well above the solid-state thermal decomposition point of AlH₂(tBuNCH₂CH₂NMe₂), which is ca. 185 °C. Similar growth rates, resistivities, and film compositions were observed in ALD film growth trials using AlH₂(tBuNCH₂CH₂NC₄H₈).