Vacancy-Type Defects and Oxygen Incorporation in NiAl for Advanced Interconnects Probed by Monoenergetic Positron Beams and Atom Probe Tomography

Positron annihilation and atom probe tomography were used to study vacancy-type defects and their interaction with oxygen in 100 nm thick NixAl1-x deposited on a SiO2/Si substrate. For as-deposited Ni0.50Al0.50, (i) monovacancy (V) and divacancy-type defects and (ii) vacancy clusters were found to coexist, and the clusters were estimated to be larger than V-10. Although no large change in the size of these vacancies was observed after postdeposition annealing below 500 degrees C, the concentration of vacancy clusters decreased as temperature increased. Upon annealing, oxygen diffused mainly through the grain boundaries. The oxygen incorporation was enhanced in NixAl1-x with high Ni contents. The consumption of Al by surface oxides under Ni-rich conditions introduced defect-rich regions, and as a result, oxygen incorporation was enhanced likely via vacancy-assisted diffusion. The incorporated oxygen tended to couple with vacancies and form vacancy-oxygen complexes that were stable at 800 degrees C annealing.