Thermochemical investigation of perspective MOCVD precursor of MgO functional layers

This paper presents a reliable and useful thermochemical information on a mixed-ligand magnesium complex with trifluoroacetylacetonate (tfac) and N,N,N′,N′-tetramethylethylenediamine (tmeda), Mg(tmeda)(tfac)2, as low melting and highly volatile precursor for metal–organic chemical vapor deposition. New vapor pressure data for sublimation and vaporization processes were obtained by Knudsen effusion and transpiration methods, respectively, giving the corresponding molar enthalpies and entropies: ∆subH328.0 = 106.2 ± 3.1 kJ mol−1 and ∆subS°328.0 = 224.8 ± 9.6 J K−1 mol−1, ∆vapH385.5 = 71.5 ± 1.4 kJ mol−1 and ∆vapS°385.5 = 131.6 ± 3.8 J K−1 mol−1. Based upon these new results, the sublimation data obtained previously by transpiration method were re-treated giving the following thermodynamic characteristics of sublimation: ∆subH345.5 = 106.4 ± 1.0 kJ mol−1 and ∆subS°345.5 = 227.4 ± 2.8 J K−1 mol−1. The thermal behavior of the precursor vapor on the heated surface in vacuum was investigated by in situ mass spectrometry in the temperature range (353–773) K. A two-step dissociation of the complex molecule was established, while no complete decomposition to form the inorganic phase was observed without reagent gases. Thermodynamic simulation of the solid phase formation from the gaseous mixture of the precursor and oxygen or water as co-reagents in Mg–O–F–C–N–H system was carried out within wide range of the deposition temperature, total pressure and reagent molar ratio in order to determine the conditions of obtaining pure MgO films.