Inhibition of interlayer diffusion and reduction of impurities in thin metal films by ion irradiation

The effect of pre-irradiation on a stack of metal multilayer thin films (MLTF) with low-energy Ar+ ions followed by thermal annealing of the stack has been studied. A three-layer Ni/Cu/V structure represented the as-fabricated MLTF samples. Each layer had a thickness of 25 nm. The entire assembly was built on Si using magnetron sputtering with different targets. The samples were pre-irradiated with Ar+ ions at 400 and 800 eV. After the irradiation, the samples were further annealed at 450 °C for 15 min in an argon atmosphere. The structure, phase, and chemical composition of the MLTF samples were examined using X-ray diffraction, Auger electron spectroscopy, and secondary ion mass spectrometry. The distribution of the primary and impurity elements in the MLTF stacks was studied before and after the treatment, determining the diffusion ability of each element and changes they cause. It was found that applying the irradiation before annealing inhibited the diffusion of Ni and V atoms into the Cu layer. In addition, samples after pre-irradiation demonstrated lower oxygen and carbon impurities in the Cu layer. The degree of oxidation in the Ni and Cu layers was also reduced. The most notable cleaning effect of the Cu layer occurred for the sample that was pre-irradiated at 800 eV.