He Chuan, Zhou Jingzhuo, Zhou Rui, Chen Cong, Jing Siyi, Mu Kaiyu, Huang Yu-Ting, Chung Chih-Chun, Cherng Sheng-Jye, Lu Yang, Tu King-Ning, Feng Shien-Ping
Department of Systems Engineering, City University of Hong Kong, Kowloon, Hong Kong, China.
Department of Mechanical Engineering, City University of Hong Kong, Kowloon, Hong Kong, China.
Nat Commun. 2024 Aug 17;15(1):7095. doi: 10.1038/s41467-024-51510-7.
Direct copper-to-copper (Cu-Cu) bonding is a promising technology for advanced electronic packaging. Nanocrystalline (NC) Cu receives increasing attention due to its unique ability to promote grain growth across the bonding interface. However, achieving sufficient grain growth still requires a high thermal budget. This study explores how reducing grain size and controlling impurity concentration in NC Cu leads to substantial grain growth at low temperatures. The fabricated NC Cu has a uniform nanograin size of around 50 nm and a low impurity level of 300 ppm. To prevent ungrown NC and void formation caused by impurity aggregation, we propose a double-layer (DL) structure comprising a normal coarse-grained (CG) layer underneath the NC layer. The CG layer, with a grain size of 1 μm and an impurity level of 3 ppm, acts as a sink, facilitating impurity diffusion from the NC layer to the CG layer. Thanks to sufficient grain growth throughout the entire NC layer, cross-interface Cu-Cu bonding becomes possible under a low thermal budget, either at 100 °C for 60 min or at 200 °C for only 5 min.
直接铜对铜（Cu-Cu）键合是一种用于先进电子封装的很有前景的技术。纳米晶（NC）铜因其独特的促进键合界面处晶粒生长的能力而受到越来越多的关注。然而，要实现足够的晶粒生长仍需要较高的热预算。本研究探讨了减小纳米晶铜的晶粒尺寸和控制杂质浓度如何导致在低温下实现大量的晶粒生长。所制备的纳米晶铜具有约50纳米的均匀纳米晶粒尺寸和300 ppm的低杂质水平。为了防止由杂质聚集导致的未生长纳米晶和空洞形成，我们提出了一种双层（DL）结构，在纳米晶层下方包含一个普通的粗晶（CG）层。粗晶层的晶粒尺寸为1微米，杂质水平为3 ppm，起到一个汇的作用，促进杂质从纳米晶层扩散到粗晶层。由于整个纳米晶层都实现了足够的晶粒生长，在低热预算下，即在100℃下60分钟或在200℃下仅5分钟，就可以实现跨界面的铜对铜键合。
