具高電遷移壽命的奈米雙晶銅導線用於重新佈線層

High Electromigration lifetimes of Nanotwinned Cu Redistribution Lines

曾億信(I.H. Tseng) ； 陳智(Chih Chen)

《鑛冶：中國鑛冶工程學會會刊》 63卷2期 (2019/06) Pp. 72-77

https://doi.org/10.30069/MM.201906_63(2).07

摘要

此實驗比較以奈米雙晶銅作為重新佈線層導線的電遷移表現以及一般銅（不具奈米雙晶銅）的電遷移表現。本團隊通過直接電流電鍍（111）優選方向的nt-Cu，電鍍條件為8A／dm^2，在溫度26℃下電鍍。以電鍍條件為12A／dm^2直流電鍍製作沒有優選晶粒方向Cu的樣品做為對照組，銅薄膜電鍍面積為1cm×3cm，厚度為3μm。電鍍之後，銅膜經歷黃光製程，製作了一條800μm長，10μm寬的Cu線，用於電遷移測試。完成樣品後，使用四點探針系統來監測RDL銅線的電遷移測試期間的電阻變化，RDL銅導線試片放在200℃加熱版持續加熱，並施加電流密度為2×10^6A／cm^2。團隊利用掃描電子顯微鏡（JEOL 7800 FESEM）中檢查銅線的優選方向以通過EDAX電子背散射衍射（EBSD）系統確認奈米雙晶銅的質量，本團隊觀察RDL銅線的微觀結構，以通過聚焦離子束（FIB）觀察孔洞分佈。發現奈米雙晶銅導線的電遷移壽命大約是一般銅導線的10倍。

關鍵字

奈米雙經銅 ； 電遷移 ； 3D IC

並列摘要

The redistribution lines (RDLs) in fan-out packages and three-dimensional integrated circuit (3D IC) become narrower resulting in the high current density in the RDLs. The three-dimensional integrated circuits could stack chips vertically and decrease RC-delay. As the scaling of large-scale ICs faced the physical limit, the IC industry was trying to follow the Moores' law to fulfill the needs of customers. The 3D IC not only reduced the form factor, but also enhanced the power efficiency. The input/output pin numbers increased while the size of the solder joints shrunk. It inevitably lead to higher current densities and operating temperatures in the joints. It raised severe reliability issues such as electromigration and thermomigration. The RDLs needed to carry higher current density than before. As the volume of 3D ICs getting smaller, copper was the critical material in interconnects. Copper has low resistivity of 1.7 μΩ, high conductivity 401 W m-1 K-1, and excellent ability to resist electromigration. The highly preferred nano-twinned copper has been studied extensively. The highly (111) oriented nanotwinned copper (nt-Cu) possesses excellent mechanical strength and high ductility. The conductivity of nt-Cu was almost the same as bulk copper. It was reported that the nano-scale twins in the copper contribute to high resistance of the electromigration. Therefore, we used nt-Cu as the material of RDL and observed destruction mechanism of electromigration tests. We also compared the electromigration lifetimes of nt-Cu RDL lines to randomly oriented Cu.

並列關鍵字

nanotwinned copper ； electromigration ； 3D IC