Effect of thin-film texture and zirconium diffusion on reliability against electromigration in chemical-vapor-deposited copper interconnects

The effects of film texture and zirconium diffusion on the reliability of chemical-vapor-deposited (CVD) copper interconnects were examined. The crystallographic orientation of CVD copper depends strongly on the substrate structure and pre-treatment sequences. Sputter pre-etching of TiN liner greatly enhanced the (111) orientation of sputter deposited copper film. The CVD copper grew epitaxially on the (111) oriented sputtered copper seed layer. Dominant impurities in CVD copper are oxygen and fluorine, which can be reduced by hydrogen annealing at 400 degrees C. By improving the texture, the lifetime against electromigration extends about twice longer than that of as-deposited CVD copper film. Copper zirconium alloy wire with a surface layer of the inter-metallic compound CuZr2 further extended the electromigration lifetime due to thermal diffusion of zirconium into copper. The electromigration lifetime of this alloy wire was significantly improved with only a small increase in electrical resistivity.