Revealing the influence of key parameters on wafer-to-wafer hybrid bonding dynamics through fluid-structure coupled simulation

In direct wafer-to-wafer (W2W) bonding process at room temperature, two silicon wafers are bonded together under the action of the short-range molecular and atomic forces at the wafer surface. However, inappropriate bonding conditions can lead to the formation of unbonded areas and large voids on the bonding surface. This paper uses a coupled solid and fluid mechanics simulation model to investigate the influence of key parameters, such as upper chuck pressure parameters, air viscosity and initial force and so on, on the dynamics of W2W bonding. The bonding initiation time, total bonding time (bonding wafer velocity) are studied in detail. The simulation results show that as the increasing of upper chuck pressure and range of pressure application, the bonding initiation time is delayed, and the total bonding time increases. When the pressure is 20 kPa and the pressure range is 0.3 R0 (wafer radius), bonding is unachievable. In addition, the increasing magnitude of the initial force (0.25 N to 0.34 N) can decrease the timing of the bonding initiation (2 s to 1 s), but its influence on the speed of the bonding propagation wave is negligible. The impact of air viscosity is the converse. When the air dynamic viscosity increased by 30%, the total bonding time was extended by 0.6 seconds. This study provides an in-depth understanding of the bonding process and help improve bonding performance further.