Elucidating the mechanism of four corner voids in chip-on-wafer hybrid bonding

In recent years, the development of electric vehicles, IoT, machine learning, and digital technologies has increased demand for high-performance and high-functionality semiconductor devices. While the performance improvement through semiconductor miniaturization to meet these demands is reaching its limit, the performance enhancement through 3D stacking of integrated circuits (ICs) has been attracting attention. One key technology in manufacturing 3D stacked structures is the chip-on-wafer (CoW) bonding process. In this study, we investigate the causes of void formation specific to the CoW bonding process. We applied bonding propagation simulation to the CoW bonding process for this investigation. We found that when the bonding wave reaches the midpoint of an edge, it progresses rapidly along the edge and generates voids by capturing air near each of the four corners.