Cu thin films were deposited by photo-MOCVD using a low-pressure Hg lamp (254 nm). Representative Cu(II) β-diketonates and Cu(I) β-diketonates have been used as molecular precursors. The influence of the photons on the growth rate, microstructure and resistivity of the films has been discussed in correlation with UV absorption spectra of the compounds. For instance, Cu deposition was found to be more significantly enhanced using Cu(thd)2 than Cu(hfa)2 due to a better wavelength match between the UV source and the ligand-to-metal charge transfer band of the former precursor. Excitation of (hfa)CuL precursors at 254 nm also results in a charge transfer from L to the metal component, which facilitates the ligand removal. The photo-energy has a lower influence on the Cu deposition from Cu(I) compared with Cu(II) compounds because of the lower thermal stability of (hfa)CuL complexes. The compound (hfa)Cu(COD) efficiently absorbs the UV radiation from the Hg lamp compared with other Cu(I) precursors. As a result, the growth rate is enhanced, and the morphology and resistivity of the films are improved using this Cu(I) precursor.
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Maury et al. (2000) studied this question.