Failure analysis of bondpads peeling problem in 0.13 μm copper process in wafer fabrication

A bondpad peeling case due to passivation residue is presented for 0.13 μm copper process in wafer fabrication (fab). It was reported that some dies from two lots of wafers failed die-pull and die shear test at the assembly house. SEM, Auger and TEM techniques were used to identify the root cause. Based on failure analysis and wafer fab investigation results, it is concluded that the peeling occurred between the barrier metal Ta and Cu layers. The root cause of the metal peeling was due to an extra thin Si₃N₄ layer between the barrier Ta and Cu layers, which could be due to passivation underetch or nitrogen flow issue during passivation layer deposition.