Following the deposition of the Metal 4 copper layer, this Cu CMP step is critical for removing the bulk copper overburden to define the isolated interconnect lines P1.The primary objective is to planarize the wafer surface and reliably stop on the underlying Ta-based liner, preparing the structure for the subsequent liner CMP step P1.Unlike earlier copper CMP steps (such as step #190) which may define finer-pitch lower metal routing, this specific upper-level BEOL step in the 40nm CIS flow must