Interface mixing induced by swift heavy ions at metal-oxide/silicon interfaces

It was observed previously that ceramic/ceramic bilayers were very sensitive with respect to the electronic stopping power S_e, i.e. strong interface mixing, scaling with , occurred if a threshold S_ec was exceeded. The threshold seemed to be determined by the higher track formation threshold of two constituents forming the bilayer. Although no track formation has been observed in crystalline Si even for Uranium projectiles, interface mixing was observed previously for some Si-multilayers.

In this paper we report on the interface mixing of NiO, Fe₂O₃, TiO₂ on Si due to irradiation with 90–350 MeV Ar-, Kr-, Xe- and Au-ions at 80 K at fluences up to 9E15 ions/cm². Interface mixing, analyzed by means of Rutherford Backscattering Spectrometry (RBS), is found for these bilayers, too. But the threshold for intermixing is significantly higher compared to the ceramic/ceramic bilayers. This observation could be an evidence for the threshold being determined by the Si-layer. In contrast to NiO/Si and Fe₂O₃/Si, where an usual random walk mixing Δσ² = kΦ was observed, the interface broadening Δσ² for TiO₂/Si is found to scale nonlinearly with the ion fluence, which indicates that mixing is driven by a chemical solid-state reaction. At higher fluences plateaus form at the low energy Ni-edge of the RBS spectra. The plateaus indicate phase formation. X-Ray diffraction spectra does not show any evidence for new crystalline phases.