面向三维高密度封装的Cu6Sn5单晶UBM的定向合成原理与可靠性研究

三维封装的焊点互连工艺是实现多芯片间系统集成的关键技术之一，其中钎料焊点下的元素扩散阻挡层（UBM）技术是三维封装焊点界面可靠性的重要保证。目前传统UBM工艺已经难以满足互连焊点对铜元素扩散阻挡的要求，而比较令人关注的Cu6Sn5UBM又因其存在晶间元素快速扩散通道，无法从根本上实现对铜元素的扩散阻挡。因此，本项目拟采用预先制备单晶Cu6Sn5种籽层，通过种籽层与铜基母相的有效焊接实现铜基表面制备Cu6Sn5单晶UBM的目标。本项目拟重点研究：（1）Cu6Sn5单晶种籽层的制备与结构表征（2）Cu6Sn5单晶种籽层与铜基焊盘冶金成形机制（3）Cu6Sn5单晶UBM的重熔可靠性；（4）Cu6Sn5单晶UBM的电迁移可靠性。研究结果将对三维高密度封装的焊点UBM工艺发展有实用价值。

Three dimensional (3D) chip-stacking technology with solder interconnections is considered to have potential to realize the multi-chip assembly for very large scale integration applications. The under-bump-metallization (UBM) process is one of the key technologies to ensure the reliability of the solder connections. As the traditional UBM process could not fulfill its requirements on the diffusion barrier properties, and the Cu6Sn5 UBM containing a large number of intergranular diffusion paths is also not a satisfactory solution, our project will explore to fabricate the Cu6Sn5 single crystal layer on the Cu substrate, in which a Cu6Sn5 single-crystal seed layer is introduced between the Cu and Sn-base solder as an UBM layer. The contents include: (1) the preparation and its characterizations of Cu6Sn5 single-crystal seed layer; (2) the mechanism of the internal reaction between the Cu6Sn5 seed and interfacial Cu6Sn5 on the Cu pad; (3) the reliability of the Cu6Sn5 single-crystal UBM during reflow; (4) the reliability of the Cu6Sn5 single-crystal UBM during electromigration. This investigation provides a good starting point for fabrication of Cu6Sn5 single-crystal UBM to commercial applications, and also has the unique significance to UBM technology development in 3D packaging.