Reliability studies of narrow Cu lines

Cu damascene lines with dimensions of 100 nm and less were prepared using adapted standard processes. For metallization standard Cu damascene processes were used, with reduced thicknesses for diffusion barrier and Cu seed layer. The lines thus obtained were subjected to electromigration tests at elevated current densities and temperatures. Early breakdowns could be observed for thin lines, while wider lines had a longer time to failure. The results indicate an underlying strong correlation between the barrier layer thickness and the time to failure.