标题: 以直流电制备奈米双晶铜及其在3D IC 封装之应用
Fabrication of nanotwinned Cu by DC electrodeposition and its application in 3D IC packaging
作者: 刘道奇
Liu, Tao-Chi
陈智
Chen, Chih
材料科学与工程学系
关键字: 奈米双晶;电镀;铜;封装;聚焦离子束;三维积体电路;nanotwins;electroplating;copper;packaging;focused ion beam;3D IC
公开日期: 2012
摘要: 本论文主要研究具[111]优选方向的奈米双晶铜材料的电镀沉积技术与其在3D IC电子接点上的应用。奈米双晶的微结构鉴定必须使用聚焦离子束技术(Focused ion beam,FIB)以及电子背向散射技术(electron backscatter diffraction,EBSD),为因应3D IC微凸块的尺度特征,我们特别发展出一种低掠角聚焦离子束研磨技术,并收录于第二章。同时也节录数种因孔洞形成导致接点失效的线路修复方法。
第三章叙述以控制电流密度与转速的制程条件,沉积具备高度优选方向以及高密度双晶体堆叠铜膜的详细方法,并且对奈米双晶铜进行详尽的微结构鉴定。相较于过去文献的结果,无论在沉积速率、晶格方向优选性均有突破性的进度。XRD绕射法分析指出:镀层中(111)绕射峰强度是(222)强度的506倍,也远高于过去文献中电镀双晶铜层的纪录。所生成的双晶晶格间距约为 10 nm到 100 nm之间,高密度的铜双晶提供优异的机械性质,机械硬度高达2.23GPa。藉由直流电镀可高速沉积20 μm的铜层厚度,使此材料非常适合用来制造3D IC 中的微凸块结构。第四章研究此奈米双晶铜在微凸块冶金反应下的行为特性。由于双晶晶界(twins boundary)上聚集着大量的原子差排与扭结可以用来作为空位阱(vacancy sink)。因此奈米双晶铜可以消除克氏孔洞(Kirkendall voids)。在实际应用于晶片封装的表现上,证实奈米双晶铜可提升接点可靠度。
克式孔洞的形成会使铜锡界面的机械强度变弱。我们藉由奈米双晶铜不会产生孔洞的特性,可以单独观察到Cu/solder/Ni 微凸块内部的交互作用对介金属化合物成长的影响。10 μm的焊锡接点内形成的镍浓度梯度,驱动镍原子快速穿透到对向端影响介金属化合物生成反应,形成比Cu6Sn5热力学性质更稳定的三元合金相的(Cu,Ni)6Sn5,因此可以减缓Cu3Sn的成长。完整的结果已收录于第五章。
This research proposed a novel approach for the fabrication of an [111]-oriented nanotwinned Cu (nt-Cu) material by utilizing electrodeposition technique and its application in microbumps of 3D IC. The material characterization of nt-Cu was performed with focused ion beam (FIB) and electron backscatter diffraction (EBSD). A developed low-angle FIB polishing technique for cross-sectioned microbumps is described in Chapter 2. In addition, several methodologies of circuits repair for the void-damaged solder joints have also herein.
Chapter 3 proposes particularly the fabrication of preferred-oriented Cu films with densely packed nanotwins with various current and stirring speeds. Furthermore, the material characterization has been completed and reported. Compare with the previous literatures, this technique provides the high deposition rate and the intensity of preferred orientated microstructure. X-ray diffraction indicates the intensity ratio of (111) to (220) is as high as 506, which is the highest among the reported electroplated Cu films. The twins spacing ranges from 10 nm to 100 nm, which reveals a high hardness value of 2.23GPa. The film thickness of nt-Cu can be grown to exceed 20 μm thick with DC electrodeposition; therefore, which possesses the capability of the manufacturing of 3D IC microbumps.
Chapter 4 demonstrates the metallurgy reaction of the nt-Cu-containing microbumps. As the high densities of steps and kinks at the nano twin boundaries which serve as vacancies sinks, the nt-Cu can eliminate the Kirkendall void. We found no formation of Kirkendall voids in solder reactions on the nano-twinned Cu. In practice, the joint reliability of chip packaging can be enhanced by nt-Cu . The formation of Kirkendall void can weaken the mechanical properties of the microbumps. Therefore, the void-free nt-Cu can be performed to observe the cross-interaction independently affecting to the interfacial reaction in Cu/solder/Ni microbump. The results indicates that the metallurgical reaction caused the Ni atoms diffusing to the Cu side to form the (Cu,Ni)6Sn5, and the growth of the Cu3Sn IMCs was inhibited due to the formation of the ternary intermetallic compounds, which possesses a lower free energy than Cu6Sn5 does. A considerable concentration gradient of Ni was detected in 10 µm solder sample, which triggers the diffusion of Ni atoms to the Cu side.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079718819
http://hdl.handle.net/11536/44949
显示于类别:Thesis