2-methyl-1-hexen-3-yne Lewis base stabilized, β-diketonate copper(I) complexes:: X-ray structures, theoretical study, and low-temperature chemical vapor deposition of copper metal

Four new beta -diketonate copper(I) complexes containing the ene-yne 2-methyl-1-hexen-3-yne (MHY), [Gu(hfac)(MHY)] (hfac = hexafluoroacetylacetonate), [Cu(tfac)(MHY)] (tfac = 1,1,1-trifluoroacetylacetonate), [Cu(pfac)(MHY)] (pfac = perfluoroacetylacetonate), and [Cu(acac)(MHY)] (acac = acetylacetonate), have been synthesized and characterized by FT-IR and H-1 and C-13 NMR and three of them by an X-ray structural and elemental analysis. In these complexes, the triple bond is eta (2)-coordinated to the copper atom while the double bond stays free. A theoretical study demonstrates that for these complexes a planar coordination around the copper ion is the most stable, with energy differences of 57.7, 44.9, 39.3, and 62.7 kJ/mol for the acac, tfac, hfac, and pfac complexes, respectively, when compared to a tetrahedral structure, which is another possible coordination mode for Cu(I). We also found that the orbital contribution of the fluorine atoms does not seem to be very relevant for the Cu-alkyne bond, but rather weak fluorine-hydrogen bonds detected in the X-ray structures can explain the following experimentally found stability order: [Cu(acac)(MHY)] < [Cu(tfac)(MHY)] < [Cu(hfac)(MHY)] = [Cu(pfac)(MHY)] The decomposition of such compounds to give Cu(0), MHY, and [Cu(beta -diketonate)(2)] seems to indicate a similar thermodynamic stability of the products. However, experimentally the complex with the pfac ligand shows a greater stability while the acac complex decomposes easily. The more stable and volatile compounds are obtained when the beta -diketonate ligand is hexafluoropentanedionate, which has been used as a precursor in copper CVD experiments. So, [Cu(hfac)(MHY)] (mp = 13.0 degreesC, bp = 207.2 degreesC), which displays a partial pressure of 110 mTorr at 21.3 degreesC, was used with 5% (wt) of pure MHY as a stabilizing agent. Using a direct liquid injection and vaporizer system, pure copper films were deposited in a cold-wall LPCVD system with helium as carrier gas on 4 in. diameter silicon wafers covered with a 200 nm thick CVD TiN film as a barrier. The copper films were deposited at a precursor vaporization temperature of 85 degreesC and deposition temperature of 140-300 degreesC. In this temperature range, the growth rate demonstrates the two usual different regimes: the mass-flow-controlled regime above 220 degreesC with a growth rate as high as 260 nm/min and the surface-limited regime below this temperature. For this last regime, the activation energy is only around 30 kJ/mol, which is a very low value when compared to what was obtained for processes using other Cu(I) beta -diketonates. Shiny, adhesive copper films with a thickness of 500-1000 nm had resistivities of 2.3-4.5 mu Omega cm, depending on the substrate temperature. ESCA analysis of the Cu layers revealed that the Cu films were very pure but contained 2.7 atom % of oxygen impurities due to leaks or residual H2O in the CVD system which were still present after 10 min of Ar sputtering.