Fabrication and Reliability Analysis of Quasi-single Crystalline Cu Joints Using Highly <111>-oriented Nanotwinned Cu

This study investigated the reliability performance between microstructure and bonding interface appearance in bonded Cu joints. Only one grain in a Cu joint is noted as "quasi-single crystal (QSC)" and it can be fabricated within a Cu joint with proper heat treatment. It might be an ideal Cu joint without bonding interface and thus the bonding strength of a chip can be increased. Die pulling tests and thermal cycling tests (TCTs) up to 1000 cycles were carried out to quantize the reliability. Results show that QSC joints provide excellent bonding reliability in pulling tests and TCT. Highly ductile fracture was observed in QSC joints and higher bonding strength was observed; whereas other joints with bonding interface showed brittle fracture. Furthermore, no cracks in QSC joints were found after 1000 cycles of TCT and the electrical resistance just slightly increased. It is inferred that bonding interface elimination acts as a key role in bonding strength increase.