High-performance vertical interconnection for high-density 3D chip stacking package

The three-dimensional (3D) chip stacking technology developed in ASET is a leading technology for realization of a high-density and high-performance system-in-package (SIP). As for the advanced interconnection technology, a 20-μm-pitch low impedance vertical interconnection through Cu through via (TV) within thin chips plays the following roles: wide signal bus and very short electrical path for high-frequency signal transmission, strong power supplies and stable ground lines. The vertical interconnection was fabricated by inter chip connection (ICC) process, which includes Cu bump bonding (CBB) utilizing Cu-Sn diffusion for connecting Cu TVs without the formation of bumps on the chip back surface and encapsulation micro thin gap between chips. We elucidate the Cu-Sn diffusion phenomena and Cu oxide influence which were important CBB issues to realize the minute interconnection of Cu TVs. The temperature cycling test (TCT) was performed on chip on chip (COC) and 3D chip stacking structures fabricated by ICC process, and over 1,000 cycles reliability was confirmed. The consistent fabrication of vertical interconnection was realized. Then, we conducted the two important electrical evaluations. One is the DC resistance of the vertical interconnection, which measured only 15.4 mΩ per layer. Another was the signal transmission delay, and only 0.9 ps was confirmed. Therefore, the vertical interconnection with Cu TV and ICC demonstrates the excellent capability of high performance interconnections on 3D chip stacking package. In addition, the micro scale strip line was evaluated to realize advanced SIP. The eye diagram on 3 Gbps indicated sufficient transmission. We will be able to realize high performance advanced SIP utilizing the vertical interconnection and high-speed horizontal line.