Low-temperature Cu-Cu bonding enabled by two-step plasma-induced Cu nitride formation and post-bond annealing

초록

The effect of post-bond annealing on the quantitative interfacial adhesion energy of low-temperature Cu-Cu bonding interfaces was systematically investigated using a double cantilever beam test. A two-step Ar/N2 plasma treatment was applied to achieve low-temperature bonding. This treatment protected the Cu surface from oxidation by forming Cu nitrides such as Cu3N and Cu4N, which were confirmed via electron backscatter diffraction and X-ray photoelectron spectroscopy analyses. Cu3N and Cu4N completely decomposed at 200 degrees C, enabling pure Cu-Cu low-temperature bonding. The interfacial adhesion energy at post-bond annealing temperatures of 250 degrees C, 300 degrees C, and 350 degrees C was 0.65 +/- 0.05 J/m2, 3.81 +/- 0.61 J/m2, and 4.12 +/- 1.12 J/m2, respectively. As the post-bond annealing temperature increased, Cu atomic diffusion was enhanced, leading to the elimination of voids and seams, grain growth, and the disappearance of grain boundaries. Consequently, the improved Cu-Cu bonding quality resulted in an increase in interfacial adhesion energy.

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