Synthesis and Development of Precursor Molecules and Reactions for Atomic Layer Deposition (ALD) of Elemental Zn and Ge

Abstract

Ultra-thin films of pure elements are important in microelectronics due to their wide range of applications. Atomic Layer Deposition (ALD) has drawn increasing attention as the thin films deposition technique for applications in microelectronics, due to its ability to deposit thin films with high conformality with atomic level control of the thickness of the film. However, due to the limited number of suitable precursor/co-reactant pairs available, only a few pure elements have been deposited successfully by ALD to date. The current study involves the synthesis and identification of potentially suitable precursor and co-reactant molecules for ALD of elemental Zn and Ge, neither of which have previously been achieved. MeZnOiPr, Zn(OiPr)2, and ZnEt2 were investigated as Zn precursors while GeCl2(Dioxane), Ge{N(SiMe3)2}2, and Ge(OCH2CH2NMe2)2 were investigated as Ge precursors. Co-reactants of interest were, 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin), PhSiH3, [H2Al(tBuNCH2CH2NMe2)] (LAlH2), BH3(NMe3), and AlH3(Quinuclidine). Ligand-exchange reactions between precursors and co-reactants were expected to produce unstable zinc or germanium hydride species, which would then reductively eliminate to produce the pure element. Solution reactivity studies were employed to identify potential precursor/co-reactant pairs. Solution reactions of Zn precursors with the selected co-reactants indicated that unstable ZnH2 is produced during the reactions, and will dissociate into its elements (Zn and H2) at room temperature. These solution reactivity studies revealed that, HBpin and LAlH2 were more reactive as co-reactants than BH3(NMe3), AlH3(Quinuclidine), and PhSiH3. Additionally, MeZnOiPr and ZnEt2 exhibited the highest reactivity as precursors, although the lower reactivity of Zn(OiPr)2 may simply be due to low solubility. Solution reactions of Ge precursors produced a polymeric mono-germanium hydride species (GeH)x, which will only dissociate into its elements upon heating at elevated temperatures. While LAlH2 indicated high reactivity with all Ge precursors, it was difficult to arrange co-reactants in order of reactivity as most reactions immediately produced insoluble (GeH)x upon mixing reagents at room temperature. Ge(OCH2CH2NMe2)2 found to be the most reactive precursor out of all Ge precursors investigated.