Impact of microstructure engineering on electromigration resistance of copper redistribution lines
Yi-Quan Lin, Yu‐Wen Hung, Dinh-Phuc Tran, Chih Chen
Abstract
In this study, the electromigration (EM) reliability and failure mechanisms of Cu redistribution lines (RDLs) with four distinct microstructures (regular Cu, nanotwinned Cu (NT-Cu), nanocrystalline Cu (NC–Cu), and annealed NT-Cu (A-NT-Cu)) were systematically investigated. EM testing was performed in ambient atmosphere at a high temperature (220 °C) under a high current density (1.0 × 10 6 A/cm 2 ). It was found that A-NT-Cu lines exhibited the longest EM lifetime, with a mean time to failure (T 50 ) of 2751 h, followed by NT-Cu (2112 h), NC-Cu (1813 h), and regular Cu (1566 h). The enhanced reliability of A-NT-Cu was attributed to its strong (111) texture and high fraction of coherent twin boundaries (CTBs), which effectively suppresses oxide formation and void generation along grain boundaries (GBs). In contrast, NC-Cu accelerated the degradation due to excessive GB diffusion, resulting in the highest hazard rate ( h(t) ) at prolonged testing durations. These findings demonstrate that microstructure engineering through NT design and texture control is a promising strategy for improving the EM reliability of Cu-RDLs in advanced microelectronic packaging.