以直流電製備奈米雙晶銅及其在3D IC 封裝之應用

Abstract

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.