Nanocrystalline copper for direct copper-to-copper bonding with improved cross-interface formation at low thermal budget

Chuan He, Jingzhuo Zhou, Rui Zhou, Cong Chen, Siyi Jing, Kaiyu Mu, Yu-Ting Huang, Chih-Chun Chung, Sheng-Jye Cherng, Yang Lu, King-Ning Tu and Shien-Ping Feng ()
Additional contact information
Chuan He: Kowloon
Jingzhuo Zhou: Kowloon
Rui Zhou: Kowloon
Cong Chen: Pokfulam
Siyi Jing: Kowloon
Kaiyu Mu: Hong Kong Science and Technology Parks
Yu-Ting Huang: Kowloon
Chih-Chun Chung: Kowloon
Sheng-Jye Cherng: Kowloon
Yang Lu: Pokfulam
King-Ning Tu: Kowloon
Shien-Ping Feng: Kowloon

Nature Communications, 2024, vol. 15, issue 1, 1-11

Abstract: Abstract 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.

Date: 2024
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DOI: 10.1038/s41467-024-51510-7

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