A study on the interaction between barrier and plating causing edge stringer defects in 28nm

In any technology, although we have an edge exclusion (usually around 3mm), defects on the extreme edge almost always kill the saleable dies inside [1][2]. For these reasons, edge defectivity reduction plays an important role on any matured technology. Edge defects include films peeling, residues from lithography steps, and many others. In this paper, one such failure mode is discussed. It will also be discussed how the interaction of two unit processes creates the defects that causes issues for downstream processing. Copper stringers are thin strands of copper wire that are seen post edge bead removal in the copper plating process. Initially thought to be coming from the plating process, detailed study supported by material and physical analysis shows the interaction of the barrier seed deposition process with the plating process resulting in the formation of stringers. It was also observed that further thinning of the barrier thickness makes the defectivity worse.