Oxidation and reduction processes in Ni/Cu/Cr/Si(100) thin films under low-energy ion irradiation

Ni(25 nm)/Cu(25 nm)/Cr(25 nm) thin films were deposited by DC magnetron sputtering at room temperature onto Si(100) single-crystal substrates and irradiated by low-energy Ar+ ions in the energy range of 400 - 2000 eV with fluences of 1.41016 - 1.11017 ion/cm2. Influence of the ion bombardment on the structural properties, surface morphology and chemical composition was investigated using XRD, AFM, SEM, AES, XPS, SIMS and SNMS techniques. It was found that the low-energy ion bombardment does not lead to phase composition modifications, but causes reduction of Ni layer crystallites size. Optimal bombardment mode (energy 800 eV, fluence 5.61016 ion/cm2), providing reduction of impurities amount in all three layers of the stack without diffusion intermixing between main components, was determined. Calculated coefficients of internal layers passivation are in good agreement with found increase of Cr and Cu layers thicknesses due to the reduction processes. New model of reduction processes taking into account the long-range effect was proposed.