Ni Barrier Symmetry Effect on Electromigration Failure Mechanism of Cu/Sn–Ag Microbump
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Ni barrier symmetry effect on the electromigration (EM) failure mechanism of Cu/Sn–Ag microbump were systematically investigated by studying the intermetallic compound (IMC) growth characteristics at 150 °C with a current density of 1.5 × 105 A/cm2. In the symmetric Ni barrier structure, Cu diffusion to Sn–Ag solder was restricted by the Ni barrier at both interfaces and the Ni3Sn4 phase formed by the inter-diffusion between Ni and Sn atoms just after bonding, which was gradually transformed to (Ni,Cu)3Sn4 phase and later to (Cu,Ni)6Sn5 during current stressing with relatively slow resistance increase with time. By the way, in the asymmetric structure, extensive Cu6Sn5 phase grew by the inter-diffusion between Cu and Sn atoms due to there is no Ni barrier at the upper interface, which was rapidly transformed into only Cu6Sn5 and Cu3Sn IMCs during electron downward flow, with relatively fast resistance increase with time. Therefore, the symmetric Ni barrier structure is very effective in restricting extensive IMC reactions during EM of Cu-solder microbump structure.
KeywordsMicrobump Symmetry Ni barrier Electromigration Intermetallic compound
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1D1A3B03933937), and also by MOTIE (Ministry of Trade, Industry and Energy (10067804) and KSRC(Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device. The authors would like to thank Dr. M.S. Suh and N.S. Kim from SK Hynix Semiconductor Inc. for valuable discussions and test sample preparations.
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