Behavior of Cu 0.6Al 0.4 films at the SiO 2 interface

Abstract

The interaction of a sputter-deposited Cu 0.6Al 0.4 film with SiO 2 (Cu 0.6Al 0.4/SiO 2) is investigated using X-ray photoelectron spectroscopy (XPS) and ex-situ scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis (EDX) capability. The data indicate that aluminum segregates to the SiO 2 interface and becomes oxidized. The formation of the aluminum oxide at the interface results in stronger chemical interaction of copper with the substrate. For copper coverages less than ∼0.31 ML (based on a Cu/O atomic ratio), only Cu(I) formation is observed. At higher coverages, Cu(0) is observed. The change in slope is coincident with the change in copper oxidation state. The adhesion behavior of copper in the Cu 0.6Al 0.4/SiO 2 case is similar to that of copper metal sputter-deposited onto α-Al 2O 3(0001). These data are in contrast with the observed behavior of copper metal deposited onto SiO 2 (Cu/SiO 2). The data for Cu/SiO 2 show that copper does not wet SiO 2 and forms 3-D nuclei. Furthermore, post-annealing experiments performed on Cu 0.6Al 0.4/SiO 2 show that neither de-wetting nor diffusion of copper occurs for temperatures up to 800 K. The data indicate that aluminum alloyed with copper at the SiO 2 interface serves as an effective adhesion promoter and thermal diffusion barrier.