Interdiffusion in copper-aluminum thin film bilayers. I. Structure and kinetics of sequential compound formation

Interdiffusion in Cu-Al thin film bilayers at temperatures between 160 and 300 °C has been studied by a combination of glancing-incidence x-ray diffraction, Rutherford backscattering spectroscopy, and transmission electron diffraction and microscopy. A sequential intermetallic compound formation was observed in samples with an excess amount of Cu with θ-CuAl2 forming first, followed by η2-CuAl, and γ2- Cu9Al4. In samples with excess Al, the θ-CuAl 2 is the first and the last phase formed. The thickening of these compounds was found to obey a parabolic relationship with time, and especially the thickening of θ-CuAl2 can be described by a prefactor of 7.4 cm2/s and an activation energy of 1.31 eV.