Metastable Fine Grain Cu for Hybrid Bonding Applications

Utilizing metastable fine-grain copper offers an opportunity to implement low-thermal budget hybrid bonding techniques. We outline several methods for characterizing fine-grain structures and a screening process to refine these structures. Furthermore, we explore the differences in copper grain evolution between blanket and patterned wafers at room temperature. Finally, we introduce metastable fine-grain copper, which demonstrates stability for four weeks of self-annealing and maintains stability through annealing at 150°C for 2 hours, with grain growth occurring at 250°C. The capability to maintain fine-grain copper over an extended period presents a promising solution for low-thermal budget hybrid bonding.