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

This study investigates the development of face-to-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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.4\ \mu \mathrm{m}$</tex> pitch. Additionally, we evaluated the connectivity of long daisy chains with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.7\ \mu \mathrm{m}$</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3\mathrm{D}$</tex> integration applications.