Thermal instability of nanocrystalline Cu enables Cu-Cu direct bonding in interconnects at low temperature

摘要

Cu-Cu direct bonding has provided an alternative packaging method to circumvent various issues that arise in conventional Cu/Sn/Cu interconnects, and has potential applications in three-dimensional integrated circuits (3D IC). However, achieving a low-temperature bonding with high integrity remains a challenge. In this paper, we demonstrate a method of low-temperature Cu to Cu direct bonding with a perfectly indistinguishable bonding interface achieved using a randomly oriented nanocrystalline Cu interlayer at 250 degrees C. No orientation control is needed to be performed to assist bonding, neither any post-bonding annealing step is required. The elimination of the bonding interface was enabled by the low thermal stability of nanocrystalline Cu at low temperatures. Microscale tensile testing of the interfacial region has shown a ductile fracture behaviour which proves excellent mechanical integrity.

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