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

Abstract

Four new β-diketonate copper(I) complexes containing the ene−yne 2-methyl-1-hexen-3-yne (MHY), [Cu(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 1H and 13C NMR and three of them by an X-ray structural and elemental analysis. In these complexes, the triple bond is η2-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(β-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 β-diketonate ligand is hexafluoropentanedionate, which has been used as a precursor in copper CVD experiments. So, [Cu(hfac)(MHY)] (mp = 13.0 °C, bp = 207.2 °C), which displays a partial pressure of 110 mTorr at 21.3 °C, 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 °C and deposition temperature of 140−300 °C. In this temperature range, the growth rate demonstrates the two usual different regimes: the mass-flow-controlled regime above 220 °C 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) β-diketonates. Shiny, adhesive copper films with a thickness of 500−1000 nm had resistivities of 2.3−4.5 μΩ 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.

Me3SiCC–CMeCH2 copper(I) β-diketonates: Synthesis, solid state structure, and low-temperature chemical vapour deposition

“…This is in agreement with the observation made in the IR spectra of 5-7 (vide supra) and is typical for other ene-yne species, i.e. [(MHY)Cu(bdiketonate)] [27].…”

“…For 5-7 relatively small Dm C"C values (5: 242, 6: 241, 7: 208 cm À1 ) are obtained showing that in 7 somewhat weaker copper-carbon alkyne bonds are present as in 5 and 6. These data correspond to other [(hfac)Cu(b-diketonate)] complexes and are in agreement with Dm C"C characteristic for [(MHY)Cu(b-diketonate)] (MHY = 2-Methyl-1-Hexen-3-Yne) [27]. Furthermore, two typical m a (CO) and m s (CO) absorptions are found between 1520 and 1660 cm À1 , whereby m a corresponds to the asymmetric and m s to the symmetric stretching vibration [27,[31][32][33][34].…”

“…These data correspond to other [(hfac)Cu(b-diketonate)] complexes and are in agreement with Dm C"C characteristic for [(MHY)Cu(b-diketonate)] (MHY = 2-Methyl-1-Hexen-3-Yne) [27]. Furthermore, two typical m a (CO) and m s (CO) absorptions are found between 1520 and 1660 cm À1 , whereby m a corresponds to the asymmetric and m s to the symmetric stretching vibration [27,[31][32][33][34]. Dm CO (Dm CO = m a À m s ) smaller than 70 cm À1 points to symmetrical, while larger values are typical for a asymmetrical bonding mode of the b-diketonates [32].…”

“…The CH fragment of the b-diketonates gives rise to one very characteristic resonance signal at 94.9 (5), 89.9 (6) or 89.6 ppm (7). The CO carbons are found between 178 and 202 ppm as it is expected for this type of building blocks [27]. It is obvious that the CO resonance signal for 7 (178.3 ppm) is significantly high field-shifted, when compared with 5 Table 2.…”

“…This unstable complex was thought to be bimetallic in which the alkyne unit binds to two copper(I) ions [26]. The formation of such species may be avoided by introducing both, p-conjugated vinyl or acetylenic units, and electron-withdrawing groups such as OCH 3 or CF 3 , respectively [27]. The best results so far could be obtained, when the alkyne unit is conjugated with a vinyl entity [28].…”