Investigation of Distortion in Wafer-to-wafer Bonding with Highly Bowed Wafers

With the trend of contact pitch scaling down, tight wafer-to-wafer overlay control is required to ensure device electrical yield performance in hybrid bonding. The backside connectivity required for the most advanced logic nodes sets a need for another metric: backside lithography overlay. Bonding-induced wafer distortion is the main contributor for both wafer-to-wafer and backside lithography overlay fingerprints. And the shape of the incoming wafer has a large impact on the distortion. The incoming device wafer warpage has an increasing trend due to the ever-increasing complexity of the functional and interconnect layers. This leads to a necessity to understand the influence of wafer shape on the bonding mechanics, which will help to find the path to minimize the wafer distortion. In this study, we investigate bonding of umbrella and bowl-shaped wafers which have a warpage up to 250μm. We employ multiple metrology methods at different stages of the processing to closely monitor wafer deformation. High-resolution wafer-to-wafer and backside post-lithography overlay signatures are analyzed.