The reservoir effect to electromigration characteristics of borderless vias was investigated. The tested samples were via chains consisting of the W plugs and AlCu lines. The AlCu line was extended over the via to a reservoir. The degradation of the EM reliability for a via without a reservoir which will cause current crowding is due to the via misalignment. In this work, we demonstrated that a long reservoir does not improve the via reliability effectively. The observation of vias showed that voids formed at various locations near the via. It is suggested that the void formation at various locations is depend on the current distribution near the via. ©1998 American Institute of Physics.