A novel Cu(II) chemical vapor deposition precursor: Synthesis, characterization, and chemical vapor deposition
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A novel Cu(II) chemical vapor deposition precursor: Synthesis, characterization, and chemical vapor deposition Anjana Devi, J. Goswami, R. Lakshmi, and S. A. Shivashankar Materials Research Centre, Indian Institute of Science, Bangalore-560 012 India
S. Chandrasekaran Department of Organic Chemistry, Indian Institute of Science, Bangalore-560 012 India (Received 13 January 1997; accepted 25 June 1997)
A nonfluorinated b-diketonate precursor, bis(t-butylacetoacetato)Cu(II) or Cu(tbaoac)2 , was synthesized by modifying bis(dipivaloylmethanato)Cu(II) or Cu(dpm)2 for chemical vapor deposition (CVD) of copper. The complex was characterized by a variety of techniques, such as melting point determination, mass spectrometry, infrared spectroscopy, elemental analysis, thermogravimetric and differential thermal analysis, and x-ray diffraction. Cu(tbaoac)2 has a higher sublimation rate than Cu(dpm)2 over the temperature range 90–150 ±C. Pyrolysis of Cu(tbaoac)2 leads to the formation of copper films at 225 ±C, compared to 330 ±C for Cu(dpm)2 . As-deposited copper films were highly dense, mirror-bright, adhered strongly to SiO2 , and showed a resistivity of ˚ A possible mechanism for the less than 2.9 mV-cm at a thickness as low as 1300 A. decomposition of the ligand tbaoac has been proposed.
I. INTRODUCTION
Chemical vapor deposition (CVD) is a versatile process for the preparation of thin films of a variety of materials, such as metals, semiconductors, oxide superconductors, and oxide ferroelectrics.1–10 Choosing the optimal precursor with high volatility and thermal stability during its evaporation and transport, and with a low reaction temperature, is a considerable challenge. Various organic ligands have been employed to synthesize metal-organic (MO) precursors, for example, the b-diketonate class of complexes like the acetylacetonates(acac), hexafluoroacetylacetonates(hfac), and dipivaloylmethanates(dpm), and alkoxides of different metals. These compounds have been used as precursors for CVD of metals like Cu, superconductors like YBa2 Cu3 O72x , and other oxides.11–15 In particular, a variety of b-diketonate complexes of copper have been investigated in recent years for suitability as precursors for the CVD of copper, a process of great potential importance in the metallization of VLSI circuits.15–21 Of these, the acac and dpm complexes have been found to be insufficiently volatile, leading to low deposition rates.22 Fluorinated Cu(I) and Cu(II) b-diketonates (hfac-based) have led both to high rates of deposition and to significantly lower deposition temperatures.23–25 However, fluorination makes precursor handling more difficult, which it is very desirable to avoid. Additionally, hfacbased Cu(I) precursors, even when ligand-stabilized, have poor thermal characteristics and short shelf life.26 The goal of the present work was therefore to design and synthesize a new b-diketonate precursor by modifying the dpm ligand, without fluorination, to J. Mater. Res., Vol. 13, No. 3,
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