Nanograin‐Twin‐Nanograin Alternating Composite Structure Enable Improved Cross‐Interface Cu─Cu Bonding at Low Thermal Budgets
Cong Chen, Cong Chen, Hui Li, Gangqiang Peng, Zeyang Zheng, Edward Dong, Jianwen Zhong, C.X. He, Yi Wang, Jia‐Syuan Chang, Zhuofei Gan, Jinwei Gao, Yu‐Ting Huang, Chih‐Ming Chen, Chih‐Ming Chen, Shien‐Ping Feng
Abstract
Chip stacking using through-silicon via (TSV) and direct copper-to-copper (Cu─Cu) bonding technology has emerged as a superior solution to overcome the limitations of Moore's law. However, conventional approaches face a fundamental trade-off: coarse-grained Cu requires high bonding temperatures (>300 °C), while nanograined Cu is unstable and tends to coarsen even at room temperature after electroplating. Here, this paradigm is broken through a unique composite copper (comp-Cu) architecture featuring alternating nanograin (ng─Cu) and (111)-oriented nanotwin (nt─Cu) domains. The nt─Cu domains, stabilized by coherent twin boundaries (CTBs), suppress room-temperature grain growth (2% resistance drifts over 15 days), while ng─Cu regions enable rapidly grain growth at 170 °C. This dual functionality facilitates atomic bridging across interfaces via two synergistic pathways: 1) grain-boundary-diffusion-dominated ng─Cu recrystallization and 2) low-activation-energy surface migration along nt─Cu (111) planes. The resulting bonded joints achieve enhanced mechanical and electrical performance: 56.4±3.6 MPa shear strength (52% > coarse Cu), 258 h electromigration lifetime (6.45× > conventional), and 3.1% resistance drift after 1,000 thermal cycles (-16-160 °C). The work not only provides a practical solution for low-thermal-budget 3D packaging but also establishes a paradigm for designing metastable composites that reconcile traditionally incompatible properties.