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

We compare Cu/M/SiO/sub 2/ (M=Cr,V and Ta) multilayers that were deposited on Si substrates. Sample resistance measurements were carried out during annealing in 80% N/sub 2/+20% H/sub 2/, N/sub 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 /spl Aring/ 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/spl deg/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/spl deg/C, Cu atoms also diffuse to the Si substrate through the Ta layer. In all systems, annealing caused many pinholes of 0.1 /spl mu/m. For technological applications, the mechanism of hole formation should be studied in detail.