Under bump metallurgy study on copper/low-k dielectrics for fine pitch flip chip packaging

Abstract

Because the semiconductor speed increases continuously, more usage of low-k dielectric materials to enhance the performance in Cu chips has taken place over the past few years. The implementation of copper (Cu) as an interconnect, in conjunction with the ultra-low-k materials as interlevel dielectrics or intermetal dielectrics in the fabrication of ultra-large-scale integrated circuits, has been used in the semiconductor community worldwide, especially for high-speed devices. The objective of this study is to investigate the under bump metallurgy (UBM) characterization with low-k dielectric material used in damascene Cu-integrated circuits. This paper focuses on electroless Ni/Au, Cu/Ta/Cu, and Ti/ Ni(V)/Cu/Au UBM fabrication on 8-in. damascene Cu wafers and flip chip package reliability with Pb-bearing and Pb-free solders. The interfacial diffusion study and bump shear test were carried out to evaluate the bump bonding, and the failure was analyzed with optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In order to investigate the thermal stability of the UBM system with Pb-free solder, high-temperature aging (above the melting temperature) was performed and each interface between the solder and UBM was observed with optical microscopy, SEM, and TEM, respectively. The failures observed and the modes are reported in the paper.

Design‐for‐reliability implementation in microelectronics packaging development

“…The types of bump materials, bump pitch and height, as well as the under bump metallagey (UBM) opening will influence the reliability life. The combination of UBM structures and the bump materials will post significant challenges in device/package reliability (Yoon et al, 2004;Jang et al, 2004;Wu et al, 2006). In addition, cautions shall be put on the corner bumps, which are preferred to be ground bumps or dummy bumps.…”

Reaction Mechanism and Mechanical Properties of the Flip-Chip Sn-3.0Ag-0.5Cu Solder Bump with Cu/Ni-xCu/Ti Underbump Metallization After Various Reflows

“…In contrast, Ni-based UBM exhibits a slower reaction rate with lead-free solders. [12][13][14] Advantages of Ni-based UBM, as compared with Cu UBM, include good corrosion resistance and superior solderability. However, some drawbacks exist, such as high residual stress problems and spalling of the intermetallic layer during reflow.…”