Irradiation-induced improvement of crystalline quality of epitaxial Cu/Si(100) films

We have demonstrated that ion-irradiation greatly improves the crystalline quality of epitaxial grown Cu films on Si(100) substrates. For the Cu/Si system, it is well known that thermal annealing is inapplicable to the improvement of the crystalline quality of the Cu films because inter-diffusion easily occurs at the Cu/Si interfaces at temperatures as low as 470 K. Accordingly, ion-irradiation is used to anneal the epitaxial Cu films. Irradiation with 0.5 MeV 28Si ions was carried out to doses ranging from 1×1016 to 4×1016 cm−2 at temperatures of 323 and 123 K. The quality of the Cu crystalline films (∼80 nm thick) was analyzed by Rutherford backscattering spectrometry/channeling (RBS/C) before and after irradiation. In the RBS/C spectra, the minimum yield at the Cu surface decreases from 90% to 42% after irradiation to 3×1016 cm−2 at 323 K. On the other hand, the minimum yield at the Cu/Si interface decreases up to 2×1016 cm−2, but increases above that dose due to the reaction between the Cu film and the Si substrate. It is found that irradiation at 123 K effectively prevents the interfacial reaction. The RBS/C analysis reveals that the improvement of the crystalline quality of the Cu film is brought about by the decrease in mosaic spread in the Cu film. Also, it is suggested that collision-induced atomic rearrangements reduce the mosaic spread in the Cu film.