Factors determining bond wave speed in wafer bonding

Abstract Wafer-level direct bonding has become a critical process for advanced 3D architectures in logic, memory, and CMOS image sensors. The minimization of the wafer distortion caused by wafer bonding is essential for a precise overlay for the subsequent backside lithography. Although numerous studies have reported a strong connection between distortion and bond wave speed, discussion of the relationship between the pre-bonding surface and the bond wave speed has been inadequate. This study aimed to clarify the latter correlation using 300 mm wafers. Through the application of surface-sensitive techniques, we found that the plasma activation process enhances the amount of Si–OH groups on the surface, thereby enhancing the bond wave speed. Conversely, high-power plasma results in a slight decrease in bond wave speed because of the influence of excessive adsorbed water. In addition, the present study reveals no correlation between bond wave speed and adherence energy.