The copper–silicon interface: Composition and interdiffusion

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The interdiffusion of Cu and Si was studied using ion scattering spectrometry (ISS) and x-ray photoelectron spectroscopy (XPS). The samples were prepared in very high vacuum (VHV) by evaporating Cu onto Ar+-cleaned and -annealed Si(111) surfaces. The surfaces were transferred directly from VHV to UHV and analyzed by ISS and XPS. Diffusion was studied at 295 K, and then at temperatures up to 825 K. A comparison of data taken at the Cu–Si interface was made with Cu3 Si. Copper and Si interdiffuse rapidly at 295 K and above; diffusion is completed in <60 min as temperatures are increased up to 825 K, depending on Cu overlayer thicknesses of 2 or 20 nm. In contrast to previously published results, our ISS and XPS data did not provide evidence for the formation of Cu3 Si at the Cu–Si interface under the range of Cu coverage (2–20 nm) and temperatures (295–825 K) studied. The Cu 2p3/2 peak shifted 0.5 eV to lower kinetic energy for Cu–Si interfaces; this peak does not shift for Cu3 Si. Furthermore, the compositions of the Cu–Si interfaces and Cu3 Si differed. Oxide-covered Si surfaces were used in some investigations for comparative purposes, and the effect of O2 exposure to the Cu–Si interface was also studied. Oxygen contamination on Si substrates was found to retard the interdiffusion process. The Cu–Si interface reacts with O2 to form oxides of Si; no Cu oxides formed.