β-Ketoiminato-based copper(ii) complexes as CVD precursors for copper and copper oxide layer formation

Abstract

The synthesis of ketoiminato copper(ii) complexes [Cu(OCRCHC(CH3)NCH2CH2X)(μ-OAc)]2 (X = NMe2: 4a, R = Me; 4b, R = Ph. X = OMe: 5, R = Me) and [Cu(OCRCHCMeNCH2CH2NEt2)(OAc)] (6, R = Me) from RC(O)CHC(CH3)N(H)CH2CH2X (X = NMe2: 1a, R = Me; 1b, R = Ph. X = NEt2: 1c, R = Me. X = OMe: 2, R = Me) and [Cu(OAc)2·H2O] (3) is reported. The molecular solid-state structures of 4-6 were determined by single crystal X-ray diffraction studies, showing that 4a,b and 5 are dimers which are set up by two [{Cu(μ-OAc)L}] (L = ketoiminato ligand) units featuring a square-planar Cu2O2 core with a distorted square-pyramidal geometry at Cu(ii). In contrast, 6 is monomeric with a tridentate-coordinated OCMeCHCMeNCH2CH2NEt2 ligand and a σ-bonded acetate group, thus inducing a square-planar environment around Cu(ii). The thermal behavior of all complexes was studied by TG (Thermogravimetry) and DSC (Differential Scanning Calorimetry) under an atmosphere of Ar and O2. Complex 4b shows the highest first onset temperature at 213 °C (under O2) and 239 °C (Ar). PXRD studies confirmed the formation of CuO under an atmosphere of O2 and Cu/Cu2O under Ar. TG-MS studies, exemplarily carried out with 4a, indicate the elimination of the ketoiminato ligands with detectable fragments such as m/z = 15, 28, 43, 44, 45, and 60 at a temperature above 250 °C. Vapor pressure measurements displayed that 5 shows the highest volatility of 3.6 mbar at 70 °C (for comparison, 4a, 1.4; 4b, 1.3; 6, 0.4 mbar) and hence 4a and 5 were used as MOCVD precursors for Cu/Cu2O deposition on Si/SiO2 at substrate temperatures of 450 °C and 510 °C. The deposition experiments were carried out under an atmosphere of nitrogen as well as oxygen. The as-obtained layers were characterized by SEM, EDX, XPS, and PXRD, showing that with oxygen as the reactive gas a mixture of metallic copper and copper(i) oxide without carbon impurities was formed, while under N2 Cu films with 53-68 mol% C contamination were produced. In a deposition experiment using precursor 5 at 510 °C under N2 a pure copper film was obtained.

Synthesis of β‐Ketoiminato Copper(II) Complexes and Their Use in Copper Deposition

“…Vapor pressure studies of 6 displayed volatility (260°C, 118.6 mbar) in the range of other copper precursors. [6,8,79] Hence, 6 was used as CVD precursor for the formation of Cu and CuO deposits. Deposition parameters have been varied to investigate the influence on the morphology of the samples.…”

“…[58][59][60][61][62][63] Further strong absorptions for 3/4 are found at 1599 and 1565 cm -1 , which can be assigned to the respective C=O and C=C stretching vibrations ARTICLE (see Experimental Section). The C=O and C=N vibrations for 6 and 8 are found at 1587 and 1503 cm -1 (6) as well as 1541 and 1514 cm -1 (8). Upon coordination of 3/4 or 7 to Cu II these bands are shifted to lower wavenumbers confirming the formation of complexes 6 and 8 [58,59,61,[64][65][66] and hence IR spectroscopy can be used to monitor the progress of the respective reaction.…”

“…Copper, for instance, is characterized by its high conductivity, low electrical resistivity, and predominant resistance to electromigration,, which are the reasons for the replacement of aluminum for the metallization in microelectronic IC , , . Also copper oxides, Cu 2 O and CuO, are of potential use in various application fields such as magnetic storage media, solar cells, sensors, batteries,, and catalysis …”

“…For the formation of copper and copper oxides several methods have been applied including electrochemical deposition,, thermal oxidation of copper, magnetron sputtering, spin‐coating, chemical beam epitaxy (CBE), atomic layer deposition (ALD), and chemical vapor deposition (CVD) , , …”

“…Commonly, copper(II) complexes are solids and need the addition of reducing agents for the deposition of pure copper films at higher temperature (>250 °C) . Examples are: Aminoalkoxides ([Cu(OCH 2 CH 2 NMe 2 ] 2 , [Cu(OC(CF 3 ) 2 CH 2 NH t Bu) 2 ]), carboxylates ([Cu 2 ( t BuNH 2 ) 2 (μ‐O 2 CR) 4 ]; R = C n F 2n+1 , n = 1, 2, 3 ··· 6) and β‐ketoiminates ([Cu(OCRCHC(Me)NCH 2 CH 2 NX 2 )(μ‐OAc)] 2 ; R = Me, Ph; X = OMe, NMe 2 ). Especially, copper(II) β‐ketoiminates are widely used as CVD precursors, due to their thermal characteristics and their good solubility in most common organic solvents , , …”