The effect of polyimide passivation on the electromigration of Cu multilayer interconnections

Abstract

Electromigration damage (EMD) is one of the major causes for the failures of interconnect. In this study, the electromigration (EM) of Cu multilayer (TiWN/Cu/TiWN) with polyimide passivation is investigated with an isothermal resistance change method. The EM measurements were carried out on a wafer level at various temperatures (170–230 °C) and current densities (2.28–4.0$MA/cm^2$). The activation energy for passivated Cu multilayer is larger than that of the unpassivated ones. The lifetime of passivated specimens are from two to 16 times those of the unpassivated ones. Resistance oscillation, which is attributed to the formation and closing of Cu gap, is observed during EM test. The TiWN interlayer helps to maintain the electrical continuity when a local Cu gap is formed. Hence, the lifetime of Cu metallization is further enhanced by the presence of the interlayer. Copper multilayer interconnect has better EMD resistance than Cu monolayer interconnect does.