Magnesium alkylamidinates have been discussed as potential Mg precursors for the CVD of magnesium-doped compound semiconductor films. For example, bis[bis(N,N'-di-tert-butylacetamidinato)magnesium and bis[bis(N,N'-diisopropylacetamidinato magnesium], sublime at 70 °C/0.05 Torr and are excellent candidates for CVD precursors of Mg-containing thin films.[[i]]
Synthesis
Bis(N,N‘-di-tert-butylacetamidinato)magnesium Mg (yield 81%), bis[bis(N,N‘-diisopropylacetamidinato)magnesium] (yield 70%), bis(N,N‘-di-tert-butylbenzamidinato)magnesium (yield 82%), and bis[bis(1-tert-butyl-3-ethylacetamidinato)magnesium] (yield 93%), were prepared as colorless crystalline solids by the reaction of anhydrous MgBr2 with 2 molar equivalents of (1,3-di-tert-butylacetamidinato)lithium, (1,3-diisopropylacetamidinato)lithium, (1,3-di-tert-butylbenzamidinato)lithium, or (1-tert-butyl-3-ethylacetamidinato)lithium, correspondingly (prepared in situ from the corresponding carbodiimide and alkyllithium) in Et2O at RT. These complexes were characterized spectrally, analytically and by single-crystal XRD for bis[bis(N,N‘-diisopropylacetamidinato)magnesium], bis(N,N‘-di-tert-butylbenzamidinato)magnesium, and bis[bis(1-tert-butyl-3-ethylacetamidinato)magnesium].
Bis[bis(N,N‘-diisopropylacetamidinato)magnesium] exists in a monomer−dimer equilibrium in toluene-d8 between −20 and +60 °C. A van't Hoff analysis of this equilibrium afforded ΔH° = −14.7 ± 0.2 kcal/mol, ΔS° = −44.9 ± 0.2 cal/(mol·K), and ΔG°(298 K) = −1.32 ± 0.2 kcal/mol.
Bis[bis(1-tert-butyl-3-ethylacetamidinato)magnesium] contains μ,η2:η1-amidinato ligands in the solid-state structure.
The new compounds were proposed as good candidates for the chemical vapor deposition of magnesium-doped group 13 compound semiconductor films.
[i] Azwana R. Sadique, Mary Jane Heeg, and Charles H. Winter, Inorg. Chem., 2001, 40 (25), pp 6349–6355, DOI: 10.1021/ic0106928, “ Monomeric and Dimeric Amidinate Complexes of Magnesium”
Bis(N,N′-tert-butylacetamidinato)magnesium ([Mg(tBu-AMD)2]) , evaporated at 80° C, was applied for the ALD growth of MgO thin films. In each ALD cycle, the dose of ([Mg(tBu-AMD)2]) was 3×10−9 moles/cm2 (resulting in3×104 Langmuirs/cycle substrate exposure to the Mg precursor) and the dose of H2O vapor was 6×10−8 moles/cm2. (resulting in exposure to water vapor 5×105 Langmuirs/cycle). Uniform, smooth layer of MgO was deposited on substrates heated to 250° C. at a deposition rate of 0.08 nanometer per cycle. A uniform, smooth layer of magnesium oxide with composition approximately MgO film with close-to stoichiometric composition was obtained on substrates heated to 250° C, resulting in a deposition rate of 0.08 nm/ cycle. [[i]]
[i] Roy G. Gordon, Booyong S. Lim, US 7557229 B2, 2009, “Atomic layer deposition using metal amidinates “, http://www.google.com/patents/US7557229