Detection of bonding voids for 3D integration

Wafer bonding is a key technology for many advanced chip technologies. For 3D integration, advanced stacking schemes and high-density packaging put a stringent requirement on the bonding reliability. Bonding quality can be characterized by the absence of voids at the bonding interface, as the voids delimit the complexity of the subsequent processing and integration steps. Therefore, in-line and non-destructive inspection techniques for void detection are crucial for early-stage detection and full process integration. In this work, we perform a comprehensive study on bonding void detection for 3D integration. We fabricate bonded Si wafers with programmed bonding voids with size from 10 nm to 20 μm. We combine different inspection and review tools, including acoustic, optical, electron beam etc., for bonding void detection at different process steps of the fabrication with different top Si thicknesses.