Evaluation of Sn(ii) aminoalkoxide precursors for atomic layer deposition of SnO thin films

Abstract

We have successfully prepared and structurally characterized a family of eight tin(ii) heteroleptic complexes, [Sn(NR2)(ON)]x(NR2= NMe2(1a-d) or N(SiMe3)2(2a-d);x= 1 or 2) and four homoleptic systems, [Sn(κ2-ON)2] (3a-d) from a series of aminoalcohols and fluorinated aminoalcohols (H{ON}) having a different number of methyl/trifluoromethyl substituents at the α-carbon atom, [HOC(R1)(R2)CH2NMe2] (R1= R2= H (H{dmae}) (a); R1= H, R2= Me (H{dmap}) (b); R1= R2= Me (H{dmamp}) (c); R1= R2= CF3(H{Fdmamp}) (d)). The synthetic route used reactions of either [Sn{N(SiMe3)2}2] or [Sn(NMe2)2] with one or two equivalents of the aminoalcohols (a-d) in dry aprotic solvents leading to elimination of amines and formation of the Sn(ii) species1a-d,2a-dand3a-drespectively. All complexes were thoroughly characterized by NMR spectroscopy (1H,13C,19F, and119Sn) as well as single-crystal X-ray diffraction studies. In all case the solid state molecular structures of the complexes have been unambiguously established: the solid state structures1a-band1care dimeric with central {Sn2N2} cores resulting from bridging {μ2-NMe2} units, in which the Sn(ii) atoms are four-coordinate. In contrast, the solid state structures of complexes1cand2a-cpossess similarly dimeric structures, with four-coordinate Sn(ii) atoms, in which the oxygen atoms of the {ON} ligand bridge two Sn(ii) centres to form dimers with a central {Sn2O2} core. Uniquely in this study,2d, [Sn(κ2-O,N-OCMe2CH2NMe2){N(SiMe3)2}] is monomeric with a three coordinate Sn(ii) centre. The homoleptic complexes3a-dare all isostructural with monomeric four-coordinate structures with disphenoidal geometries. Solution state NMR studies reveal complicated ligand exchange processes in the case of the heteroleptic complexes1a-dand2a-d. Contrastingly, the homoleptic systems3a-dshow no such behaviour. While complexes1a-dand2a-ddisplayed either poor thermal stability or multistep thermal decomposition processes, the thermal behaviour of the homoleptic complexes,3a-d, was investigated in order to determine the effects, if any, of the degree of fluorination and asymmetry of the aminoalkoxide ligands on the suitability of these complexes as ALD precursors for the deposition of SnO thin films.