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Indexed by:期刊论文

Date of Publication:2013-10-01

Journal:JOURNAL OF ELECTRONIC MATERIALS

Included Journals:SCIE、EI、Scopus

Volume:42

Issue:10

Page Number:2975-2982

ISSN No.:0361-5235

Key Words:Electromigration; reverse polarity effect; Cu/Sn-9 wt.%Zn/Cu interconnect; effective charge number; interfacial reaction; intermetallic compound

Abstract:The diffusion behavior of Zn atoms and the interfacial reaction in Cu/Sn-9 wt.%Zn/Cu interconnects undergoing liquid-solid electromigration were investigated under a current density of 5.0 x 10(3) A/cm(2) at 230A degrees C. A reverse polarity effect was revealed, in which the interfacial intermetallic compounds (IMCs) at the cathode grew continuously and were remarkably thicker than those at the anode. This behavior resulted from the directional migration of Zn atoms from the anode towards the cathode, which was induced by the positive effective charge number (Z (*)) of the Zn atoms rather than by back-stress. Consequently, at the anode, dissolution and massive spalling of the Cu-Zn IMCs occurred, and the depletion of Zn atoms resulted in the transformation of initial interfacial Cu5Zn8 IMC into (Cu6Sn5 + CuZn); at the cathode, the interfacial Cu5Zn8 IMC gradually transformed into (Cu5Zn8 + CuZn); in the solder, the Zn content reduced continuously from 9 wt.% to 0.9 wt.%. A growth model is proposed to explain the reverse polarity effect, and the average Z (*) of Zn atoms in Cu5Zn8 was calculated to be +0.25 using this model.