Mechanistic Studies of Copper Thin-Film Growth from Cu^I and Cu^II β-Diketonates

The kinetics and mechanism of copper film growth from the reactions of bis(acetylacetonato)copper(II), bis-(hexafluoroacetylacetonato)copper(II), and (vinyltrimethylsilane)(hexafluoroacetylacetonato)copper(I) (Cu(hfac)(vtms)) with copper single crystal surfaces were investigated. Experiments were performed using vibrational spectroscopy (reflection infrared and high-resolution electron energy loss spectroscopies) as well as mass spectrometry (temperature-programmed desorption and integrated desorption mass spectrometries). Both ligand desorption and dissociation were observed upon pyrolysis of these molecules under ultra-high-vacuum conditions. We demonstrate that adsorbed β-diketonate ligands decompose in a stepwise fashion at temperatures above ∼375 K to yield adsorbed CF₃ and ketenylidene (≡C—C≡O) intermediates. These further decompose above ∼500 K to leave surface carbon, a major contaminant in copper films grown from Cu^II β-diketonates. Clean films can be grown from the pyrolysis of Cu(hfac)(vtms) at pressures above 10⁻⁵ Torr, however. The implications of our results relative to the mechanism of copper film growth at elevated pressures are also discussed.