Development of Fine-Pitch Cu-Cu Hybrid Bonding on Face-to-Back Structure for Three-Layer WoWoW: Impact of wafer-warpage on wafer bonding properties

Abstract

This study investigates the development of faceto-back Cu-Cu hybrid bonding in a three-layer structure and evaluates the impact of wafer warpage on its bonding properties. We examined fine and large-scale Cu-Cu connections with a pitch of 1.4 μm and two million connections, establishing two warpage levels: Process A and Process B. The results showed that Process A had poorer alignment accuracy, leading to open
defects at a 1.4 μm pitch. Additionally, we evaluated the connectivity of long daisy chains with 0.7 μm pads, achieving over 90 % yield. This research highlights the importance of managing wafer warpage to enhance bonding precision and electrical performance, providing insights for future
advancements in 3D integration applications.

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