Electromigration Reliability Analysis of Fine Line RDL Damascene Interconnects

In recent years, with the rapid development of Artificial intelligence (AI) technology and Moore's Law reaching its limits, advanced packaging technologies have emerged as critical for chiplets integration. Advanced packaging technologies such as CoWS, hybrid bonding, glass substrate packaging, and photonic packaging all aim to maximize the number of connections in each area, allowing signals to be transmitted quickly. For 3D stacking, TSV and Cu-to-Cu hybrid bonding are key technologies. In the case of interconnections between planar wafers, Cu Redistribution Layer (RDLs) play an important role. To achieve faster signal transmission and enhance AI computing, it is necessary to design smaller and denser Cu RDLs to meet the required specifications. As Cu RDLs become denser and demand higher current application, the electromigration of Cu becomes a critical reliability test. In this study, 1 mm-long Cu RDLs and Cu RDLs with 1 µm vias were fabricated using the damascene process, and accelerated electromigration tests were conducted by applying a high current density of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> A/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in an oven at 150°C. The experimental results show that the resistance change trends and time-dependent graphs are similar for both structures driven by electromigration. There are two main stages: a continuous rise in resistance followed by a sudden increase in resistance until the circuit is broken. The electromigration damage modes yielded very different results for the two designs. For the 1 mm-long Cu RDL, the longer structure generates significant thermal effects when driven by current, resulting in a large amount of heat accumulating at the center of the Cu RDL, which eventually leads to damage. In the case of the Cu RDL with the 1 µm-CD via, the copper atoms in the via eventually form a void in the PI layer of the via due to electron migration, ultimately losing the connection with the M1 RDL and causing a circuit break.