Influence of oxygen on diffusion in the Cu/Mo/Au system

The annealing behaviour of the Cu/Mo/Au metallization system is investigated. Backscattering spectrometry reveals a rapid diffusion of Cu and Au across the Mo film and the formation of AuCu after annealing at 600°C for 30 min in vacuum, but only when no impurity is detected in the as-deposited polycrystalline Mo layer. The Au-Cu interaction is impeded when 5.5 at% of oxygen is introduced in the as-deposited Mo layer. The thin film microstructures are analyzed using X-ray diffraction and transmission electron microscopy. The thermal stability difference between the samples with a pure Mo layer and a contaminated Mo layer is discussed in terms of fast diffusion process inhibited by a grain boundary decoration with oxygen atoms.