In back-end-of-line (BEOL) processing, conductive interconnects are formed using a damascene process where trenches and vias are subsequently filled with copper (Cu) A1.Following the MET4 trench etch and post-ash clean, this deposition step forms a Ta-based liner to completely surround and isolate the target Cu interconnect A1.Without this diffusion limiting layer, Cu atoms can easily migrate into the surrounding inter-layer dielectric (ILD), where they create deep trap states or reagglomerate t