Synthesis of heteroleptic [Sr(ddemap)(tmhd)]2 and its use in atomic layer deposition of low carbon SrO thin films

Abstract

New strontium heteroleptic complexes were synthesized by the substitution reaction of the bis(trimethylsilyl)amide of Sr(btsa)₂·2DME with aminoalkoxide and β-diketonate ligands (btsa = bis(trimethylsilyl)amide, DME = 1,2-dimethoxyethane). Three compounds, [Sr(ddemap)(tmhd)]₂ (1), [Sr(ddemmp)(tmhd)] (2), and [Sr(ddemamb)(tmhd)]₂ (3), were obtained as precursors for SrO growth (ddemap = 1-(dimethylamino)-5-((2-(dimethylamino)ethyl)(methyl)amino)pentan-3-ol, ddemmp = 1-(dimethylamino)-5-((2-(dimethylamino)ethyl)(methyl)amino)-3-methylpentan-3-ol, ddemamb = 1-(dimethylamino)-2-(((2-(dimethylamino)ethyl)(methyl)amino)methyl)butan-2-ol). In single crystal X-ray crystallography, complex 1 showed dimeric structure with µ₂-O bonds of ddemap ligand. Complexes 1 and 2 displayed high volatility and can be sublimed under reduced pressure (0.7 torr) at 150 °C. Accordingly, complex 1 was used as an atomic layer deposition (ALD) precursor for synthesis of SrO thin film at a high temperature of 370 °C. With O₃ as the oxygen source, typical ALD growth behavior was obtained with controllable initial growth and uniformity. The as-deposited SrO film reacted with carbon in the air and formed SrCO₃ with high crystallinity and poor surface morphology. However, the Al₂O₃ capping layer induced a smooth amorphous SrO film with little carbon or nitrogen impurities, which indicated the high purity of as-grown SrO film with no carbonate phase formation by the novel SrO ALD process.