Self aligned passivation of Cu in Cu/Cr, Cu/V and Cu/Ta multilayers

We compare Cu/M/SiO₂ (M=Cr,V and Ta) multilayers that were deposited on Si substrates. Sample resistance measurements were carried out during annealing in 80% N₂+20% H₂, N ₂ and Ar environments. Resistivity measurements, SEM observations, RBS and AES spectroscopies from annealed samples showed good diffusion barrier properties for Cr and V but rather poor properties for Ta buffer layers. This is due to the amorphous nature of Cr films and formation of a continuous Cu overlayer. SEM observation also showed granular structure for Cu/V and Cu/Ta with grain sizes of about 500 and 1000 Å respectively. However, shallow nitrogen implantation in Cu/V samples and DC biasing for Cu/Ta layers during deposition could enhance the adhesion and quality of the copper films. Annealing the samples in a pure nitrogen environment not only improved conductivity but annealing at 500°C for 30 minutes also resulted in diffusion of metals towards the Cu surface. Interaction of metals with the nitrogen produces a passive nitride layer. At T=600°C, Cu atoms also diffuse to the Si substrate through the Ta layer. In all systems, annealing caused many pinholes of 0.1 μm. For technological applications, the mechanism of hole formation should be studied in detail