Stable and volatile β-diketonate complexes of copper, calcium, strontium, barium and yttrium for use as chemical vapour deposition precursors



The new β-diketone 1,1,1,2,2,3,3,7,7,8,8,9,9,9-tetradecafluorononane-4,6-dione (HTDFND) has been prepared and employed in the formation of complexes of Cu, Ca, Sr, Ba and Y. Complexes of the same metals derived from the β-diketone 1,1,1,2,2,3,3,7,7,7-decafluoroheptane-2,4-dione (HDFHD) have also been prepared. In general the compounds have the formula [M(TDFND)2H2O] or [M(DHFD)2H2O], although the yttrium complexes are [Y(β-diket)3] · xH2O (β-diket ≡ TDFND (x = 3) or DFHD (x = 2)). The complexes have been characterised by analytical and spectroscopic means and by a crystal structure of [Cu(TDFND)2EtOH] obtained by recrystallisation of [Cu(TDFND)2H2O] from aqueous ethanol. Crystal data for [Cu(TDFND)2EtOH]: triclinic, P̄1, a = 11.249(4) Å, b = 12.331 (2) Å, c = 12.890(2) Å, α = 96.89(2)°, β = 108.93(3)°, γ = 109.63(3)°, V = 1541.54 Å3, Z = 2. The complex is square pyramidal with the four oxygen atoms of the β-diketonates occupying the basal sites and the oxygen atom of the co-ordinated ethanol molecule in the apical position. The C3F7 ligands take up an extended staggered configuration in order to minimise steric repulsions. The complex is monomeric with intermolecular distances all greater than 4 Å. Simultaneous thermal analysis at 1 atm reveals that all the compounds lose water but then sublime, usually completely without decomposition. [Ba(TDFND)2H2O] is the first barium complex for which this is the case and it can be dehydrated to give [Ba(TDFND)2], which is also volatile but becomes less volatile with time. [Ba(TDFND)2H2O], [Sr(TDFND)2H2O] and [Ca(DFHD)2H2O] are suitable precursors for the growth of MF2 on silicon substrates. Complete orientation in the (111) direction is observed. Changes in the film growth rate with time for all the precursors are attributed to sample decomposition ([M(DFHD)2H2O], M ≡ Ca or Sr) or to slow reorganisation of the crystal structure ([Ba(TDFND)2H2O]). Layers with Y:Ba:Cu ratios close to the required 1:2:3 have been grown using [Y(DPM)3], [Cu(DPM)2] and [Ba(DFHD)2H2O] (DPM ≡ 2,2,6,6-tetramethylheptane-3,5-dionato).