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research-article

Study on BEOL failures in a Chip by Shear Tests of Copper Pillar Bumps

[+] Author and Article Information
Lei Wang

Institute of Electronic and Electrical, Changzhou College of Information Technology, Changzhou, Jiangsu, 213164, China; Department of Materials Science, Fudan University, Shanghai, 200433, China
wl_gucas@163.com

J. Wang

Institute of Electronic and Electrical, Changzhou College of Information Technology, Changzhou, Jiangsu, 213164, China
jun_wang@fudan.edu.cn

Fei Xiao

Department of Materials Science, Fudan University, Shanghai, 200433, China
feixiao@fudan.edu.cn

1Corresponding author.

ASME doi:10.1115/1.4041714 History: Received May 06, 2018; Revised October 05, 2018

Abstract

A chip with 40 nm technology node and beyond generally incorporates low-k/ultra-low-k dielectric materials and copper traces in the back end of line (BEOL) to improve its electrical performance. Owing to the fragile low-k/ultra-low-k materials, the BEOL becomes vulnerable to external loadings. When a copper pillar bump (CPB) above the BEOL sustains a shear stress due to thermal mismatch between the components, failures occur in the microstructures of BEOL, especially in low-k materials. In this study, we fabricated CPBs on the chips and investigated fractures in the BEOL for a single CPB by a shear test approach. The parameters of shear tests, e.g. shear speed and shear height, are varied to examine their effects. The tested samples were analyzed via FIB and SEM techniques to reveal the microstructures degradation or breaks in the BEOL, which are classified into three kinds of failure modes. Assisted by a finite element analysis, the failure mechanism was explained and associated with the failure modes. The studies showed that the shear speed has a little influence on the maximum shear stress, but the increase of shear height leads to more fractures in the low-k materials. It indicated that decreasing the height of CPBs is helpful for reducing destruction risk of the BEOL beneath the CPB that is under a shear loading. The shear test of a CPB can help to evaluate the integrity of BEOL in a chip.

Copyright (c) 2018 by ASME
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