Current-Assisted Cu-Cu Bonding at Low Temperature: Process Window and Mechanism

초록

Copper-to-copper (Cu-Cu) bonding is a key interconnection technology for advanced electronic packaging; however, conventional thermo-compression bonding typically requires temperatures near 300 °C to achieve continuous and void-free interfaces. Such elevated temperatures can limit process flexibility and integration compatibility. In this study, current-assisted Cu-Cu bonding was systematically investigated under identical bonding pressure and processing time conditions to examine the role of electrical current as an additional driving force during bonding. Cross-sectional focused ion beam (FIB) analysis reveals that thermal-only bonding exhibits a threshold behavior: partial interfacial discontinuities and voids are observed at 250 °C, whereas a continuous interface is achieved at 300 °C. In contrast, the application of a 40 A electrical current enables robust interfacial bonding under modified temperature conditions, demonstrating an expansion of the viable bonding window. Electron backscatter diffraction (EBSD) analysis further shows that electrical current induces pronounced microstructural evolution and significant grain growth compared to both as-deposited and thermally annealed Cu. These results indicate that electrical current can act as an additional driving force to promote interfacial evolution during Cu-Cu bonding, offering an alternative processing approach for advanced packaging applications. © 2026 IEEE.

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