Magnesium β-ketoiminates as CVD precursors for MgO formation

Abstract

The synthesis and characterization of bis(ketoiminato)magnesium(II) complexes of composition [Mg(OCR²CH₂CHR¹NCH₂CH₂X)₂] (X = NMe₂: 3a, R¹ = R² = Me; 3b, R¹ = Me, R² = Ph. X = OMe: 3c, R¹ = R² = Me) are reported. Complexes 3a–c are accessible by the reaction of C(O)R²CH₂CHR¹N(H)CH₂CH₂X (X = NMe₂: 1a, R¹ = R² = Me; 1b, R¹ = Me, R² = Ph. X = OMe: 1c, R¹ = R² = Me) with MgⁿBu₂. The structure of 3b in the solid state was determined by a single crystal X-ray diffraction study, confirming that the Mg(II) ion is hexa-coordinated by two ketoiminato ligands, while each of the latter coordinates with its two N- and one O-donor atom in an octahedral MgN₆O₂ coordination environment in the OC-6-33 stereo-isomeric form. The thermal behavior of 3a–c was studied by TG and DSC under an atmosphere of Ar and O₂ respectively. The respective Me-substituted complexes 3a,c decompose at lower temperatures (3a, 166 °C; 3c, 233 °C) than the phenyl derivative 3b (243 °C). PXRD studies indicate the formation of MgO. Additionally, TG-MS studies were exemplarily carried out for 3a, indicating the release of the ketoiminato ligands. Vapor pressure measurements were conducted at 80 °C, whereby 3a,c possess with 5.6 mbar (3a) and 2.0 mbar (3c) significantly higher volatilities than 3b (0.07 mbar). Complexes 3a–c were used as MOCVD precursors for the deposition of thin MgO films on silicon substrates. It was found that only with 3a,c thin, dense and rather granulated MgO layers of thicknesses between 28–147 nm were produced. The as-deposited MgO layers were characterized by SEM, EDX, and XPS measurements and the thicknesses of the as-deposited layers were measured by Ellipsometry and SEM cross-section images. Apart from magnesium and oxygen a carbon content between 3–4 mol% was determined.